All right. I just loved the cinematic; but something that struct me: the "Crusade Fleet" was composed of a few huge behemot ships and plenty of support vessels around them. Something that rarely happens in my previous GalCiv games; as the game always played with this simple fact: bigger is better. Therefore, you ended up with a fleet of Cruisers at the end.
It's not as impressive, in my humble opinion, as a properly constructed (and somewhat realistic) fleet. It's always funnier to see smaller starships in operation buzzing around their bigger counterparts; akin to Destroyers and Frigates protecting their aircraft carriers. Which is why I would like to suggest to the developpers to.. well, add a layer of complexity to fleet design that would favor diversified fleets over monoclass ones. How? It's actually elegant:
Make starships deadlier as they get smaller.
Now listen. I am not promoting the idea of all-starfighters (or Corvettes) fleets. Nor am I saying that a starfighter alone should be more powerful than a starship of bigger size. It's all about cost-efficiency: the industrial production required to build 1 corvette could be better spent to build 4 starfighters, if ALL you are looking for is punch power. When it comes to Cost vs Cost, Starfighters are ALWAYS going to be superior to Corvette, who will ALWAYS be superior to Destroyers, etc...
But why build larger starships at all, then? Again, the solution is elegant:
Make certain component only available of ships of a certain class or bigger
Stuff like "Starfighter Hangar" should only be available for the biggest starships. "Anti-capital ships torpedoes" and "Flak Turrets" would be available only to Frigates. "Long-range Plasma Beam" only available to Destroyers, etc...
You will end up with starship classes with a specific mission, and it will make sense for you to make them work as a team. It will make sense for you to keep them in formation. It will make sense for your heavy weaponry to target the smallest ships first; as they are the one carrying the heaviest weaponry load.
Now, let's try to simulate, logically, what would a "comprehensive" fleet look like.
First of all, the punches: the Starfighter. They are the fastest and deadliest crafts. However, their weapons are short-range and have to expose themselves to reach their targets. There can be multiple kinds of Starfighter; from Interceptor to Bombers. A squadron of Starfighter carrying weapon X (torpedo, laser, etc..) is going to be the most cost/effective way of carrying destruction, no matter the potential hull size.
Starfighters are, ultimately, short ranged. So you need a Carrier to move them around. This can be armed, in which case it becomes the equivalent of a Battlestar. But then, why have them carry offensive weapons if it would be cheaper to have the same weapons carried by smaller starships?
Ultimately, however, a Carrier is obviously very vulnerable to Fighter strikes. Unless your contingent is specifically made up of Interceptors, you will suffer bad casualties from the opposition's fighters. This is why you need specific anti-fighter weaponry to screen against opposition attacks; like Flak Turrets or Mines. These do not fit on a Starfighter; so you need to have Frigates to deploy them around, as we have established the smaller crafts are the most effective way of carrying weaponries.
Now, we have a very interesting fleet disposition. A Carrier sorrounded by Frigates who shield it against ennemy Fighters. Thing is, with the Frigate screen, nobody has the capacity to hurt the other side with its fighter. You need a certain amount of long-range weaponry capable of punching through the frigate screen to open the way for your starfighters without exposing themselves to the ennemy's starfighters. These can only be carried around by Destroyers and bigger ships. Obviously, you could load these up on the Carrier, but it's more cost-efficient to just build Destroyers.
So we end up with:
Frigates (fighter screens)
You end up with a naturally diversified fleet. It would make sense for your Destroyers to target the ennemy's Frigates first, instead of going all-in on the carrier.