The simplistic combat of the last two games acts as a as a barrier to a lot of things. I think it's the reason combat is such a hot topic. Is it likely to change? Your guess is as good as mine.

You know, if you want to encourage the use of small hulls, you could make it so only small hulls can cross asteroid fields. (Maybe inversely only allow big hulls to cross nebula.) The possible screen shot showed asteroids acting as rivers. Being long stings between the hexes.

Well, there is certainly potential in giving certain starship class advantages in certain terrain. As long as it's logical and make sense.

I was just hoping to have a "grand strategy" need to diversified fleets. After all, as simplistic as Europa Universalis 3's combat was, it still made sense to have armies composed of a healthy mix of cavalry, infantry and cannons. 

Obviously, the game's combat mechanic will have to be revamped entirely. You are 100% right; the old system favored bigger ships.

I think one big problem is the trope named "critical existence failure"; where a starship would still perform and fight at 100% capacity even when down to its last hit point. When I think of it; I believe the solution would be to have a ship's system failure occur much, much before its hull breakdown. For example; a ship down to 80% hit point would only have 50% weapon power available. A ship down to 50% hit points would suffer a complete weapon shutdown. A ship down to 30% would be immobilized; unable to flee until emergency repairs are done.

That would suddenly make the involvement of smaller ships more combat-effective. Imagine a Battlecruiser vs. 5 corvettes; both having relatively same amount of his point and weapons in total (they hit for 20 damage total per turn, and each side have a total of 100 hit point).

The old system woud advantage the Battlecruiser big time: After 1 volley, the Battlecruiser would still be at 100% weapon capacity, while the flotilla would only be able to do 16 damage; losing 20% of its firepower. After the next round, it would just get worst for the Corvettes. Compound this problem with the problems you have outlined; it's obvious why larger starships are favored.

In my new proposed system; after the initial volley, the Corvettes would be down to 80% of their firepower while the Battlecruiser (down to 80% hit point) would be down to 50% of its initial firepower. It's easy to figure out why the Flotilla would gain the advantage. Ultimately, a diversified base for your firepower would prevent its easy crippling.

IF you are wondering why we shouldn't just have a linear diminishing of firepower following a starship's hull loss, then you just made both fleet equivalent. However, the point you made regarding Defense Advantage would make the game favoring larger starships as well. IT should become a game of balancing out individual starship's survivability with a fleet's capacity to have firepower lasting through multiple roungs.

What if a Military personal resource was introduced

a fighter would need only 1 pilot where a massive battleship would need over 1000 people to make it run properly

this could also have alot of differnt mechanics in it if your main fleet is destoryed you not only loose the fleet but 100k of your soldiers just died you people are not happy with your millitary incompitance

could also have buildings to increase how fast you recruit new troops faster even galactic projects to give you a boost maybe a slider to set how much of your population is conscipted for more evil empires with good empires getting bonus to recruitment when there at war because of patriotic pride in there empire

if you had to worry about not just the cost but also how many people you had to pilot your ships you may have to put a more balanced fleet of ships together

We could have certain ship modules or utility that require a larger chassis to carry. New high-tech SuperRailCannon requires to be installed on a battlecruiser, for example? Or some special weapons that change the battlefield (AoE weapons, maybe? Less direct damage tho) require bigger ships.

The important part is to have two "needs" that both pull in each direction of Smaller vs. Bigger. The player should compromise and adopt a fleet made of both for the optimal fleet composition. If your mechanic entirely favor big or entirely favor small ships would ruin the outome that we are looking for.

This is, unfortunately, difficult to justify when you can have a single transport ship carrying 1 billion soldiers, and it costs less than anything else in your navy (this is under the GCII model, mind you). If you can spare 500 million people for an army in just one basic transport module, you shouldn't have any problem whatsoever finding a few thousand people to serve in the navy.

Beyond that, judging by historical military levels, human nations can sustain ~5-10% of their adult population as members of the military during peacetime, and upwards of 40% during wartime. If we're looking at a multi-planet empire and considering only the requirements of the space navy, well, I think you're well within your <10% limit of peacetime military personnel even if you have hundreds of millions of people in the navy (which, judging from the crew requirements listed in GCII's intelligence report under the 'details' menu for ships, would mean that you have tens of thousands, or even hundreds of thousands, of ships).

The whole "100K soldiers died causes huge morale hit" thing is terrible when the invasion of planets requires you to bring troops in quantities similar to the total population of the planet being invaded, since the resultant casualties tend to number in the billions (or at least hundreds of millions) even on the winning side; conversely, it should hardly matter for fleet engagements that don't involve troop transports or colony ships, because individual ships rarely have crews much over a couple thousand, according to the intelligence report screen under unit details.

I could see Carriers introduced as a way to extend the operating range of little ships - instead of having to have your 10 sectors worth of life support units on every ship, you could instead have a single ship with lots of life support modules that also has 'hangar bays' which would allow your fleet to ignore the life support limits (or average the carrier and supported ships life support range in some fashion) on X of your ships below size Y (possibly up to X 'ship points', where Tiny costs A ship points, Small costs B ship points, etc, potentially with a maximum size per hangar bay/cargo module/whatever you want to call it), as well as allowing you to ignore the speed limits for those ships that fit into the hangar (which would also allow a similar module that doesn't allow you to ignore the speed limit of the little ships, which would fall into a 'fleet tender' style role). Or they could introduce a more complicated support module where each ship can carry so many supplies or so much fuel, and various types of hangar bays or other support modules allow you to extend the fleet range.

I tend to disagree with the premise that smaller ships should be deadlier, depending on implementation - I absolutely do not want to see a return to the module size scaling of GCII, not when there was no reasonable explanation for it. If weapon A does X damage no matter what ship it's on, and the game doesn't model ammunition restrictions in any way, there's absolutely no reason for weapon A to take up more space on larger hulls than on smaller hulls. Defenses I'm a bit more okay with size scaling - it makes sense that the armor plating on a battleship takes more space than the armor plating on a fighter, and it makes sense that it might take larger shield generators or more chaff dispensers to adequately protect a cruiser than a corvette; same goes for life support and engines. But weapons? My Death Ray takes less space on a fighter than on a Battleship despite there being no apparent difference due to the ship type mounting it? If my fighter Death Rays were weaker than my Battleship Death Rays, I could understand it, but not when they're functionally identical. I would tend to say that smaller ships should be more focused on firepower than survivability, and that the game mechanics should allow you to swarm big ships which aren't designed to deal with little ships in such a way as to give the little ships an advantage (overkill on big guns with long cooldowns, targeting difficulties of some kind, blind spots in fields of fire, something), but at the cost of making the little ships relatively fragile. GCII gave weapons perfect accuracy, and additionally gave big ships the defense and health advantage over swarms of little ships, and when it started allowing ships to target multiple units in any given round it took away the overkill factor which helped swarms survive.

I think it's a very good idea to have some weapons of such a size that they cannot be mounted on smaller vessels, as long as these weapons aren't made impractical due to it being better to mount 5 Fighter Laser Cannons in the place of 1 Cruiser Hypervelocity Gun or some such situation (I wouldn't mind that there might be scenarios in which that might be the better option, but I would want them to be special case scenarios - i.e. when creating an Anti-Fighter Cruiser instead of your standard Heavy Cruiser).

I still prefer the idea that groups of smaller ships should be more powerful than a larger ship. Buck for bucks, smaller ship are going to give you bigger punch.

But larger weapons have special qualities; longer range perhaps. Or AoE. Or special anti-Capital or special anti-fighter. Which justify the appearance of larger vessels on the battlefield, but does not invalidate the presence of smaller ships.

This

If you want a carrier type fleet do what I do I build 1xlarge/huge hull as the "Carrier" and use tiny/small hulls as fighters/bombers.

I re-state "IT aint broke dont fix it!" if you want proper carriers go play sins they have them on there.