Well ... Playing a custom race with popularity and likability at -30% to offset some other bonuses to try to make a race that can go toe to toe with the BORG was not a good idea. Added to the diplomacy changes all factions declared war on me almost immediately after encountering me so i ended up getting wiped out by a war on four fronts with the BORG, Tholians, Dominion and Klingons. The BORG are SERIOUSLY overpowered coming at me with ships that were pretty much indestructible by turn 145 for example having cubes with 300 missile, 120 shield, 120 point defense and 104 armor against which my best battlecruisers had a max of 96 beam and 28 on all defences. The Dominion are no slouch either. BORG planets are also incredibly hard to invade and if they happen to have the right counter to your invasion tech you can pretty much throw in the towel.
What difficulty are you playing?
The Borg will take weapon/defense Techs over anything else. It is how I set their weights up in the tech tree. So you can pretty much take it for granted they have top of the line ships, I reduced the upgrade time for the AI too, this might have be making them too OP. But Borg and Dominion should be the toughest. Who want to take over a planet of Borg? 
. I can however look at changing the default resistance.
Did you notice if the AI was attacking more than once with a fleet? This change in 1.81 could also of made my changes even more OP.
I am so sorry but your post brought a huge smile to my face, I lose 3 out of 4 games on gifted. When I first made the Borg they were such push overs it made me cry
Horemvore, would it be possible to make the benevolent and pragmatic races more inclined to ally once the BORG get too strong ? Not sure how or if that can be done but it would give at least a chance of survival on higher difficulties. As it stands now i think the only way to ensure other races DOW the BORG is to lose the home planet while having the appropriate pragmatic ideology trait. That's a big sacrifice to make.
Could a benevolent choice down the tree be created that gets all benevolent/pragmatic races to ally together against cybernetic races? Maybe a building like the "Federation Council" that gives the owner presidency of the united planets with a new diplomatic option to form an alliance against the BORG, to get really complicated the evil races could have the option to abstain but not veto.
This is something I want or at least a similar mechanic for both the Borg and Dominion. I just, have not looked into the code yet to see if it is possible. I normally see the Borg at war with at least 2 factions in my games, not including myself. I can maybe add a Hate line for the rest of the factions to hate the Borg.
Might be an idea for a scenario ....
We can not do Scenarios/Campaigns yet as modders 
However, a Mega Event could be possible or even just a Standard event. I will look at the code an see what I can come up with.
BTW this is the Federation faction I use. FEDFaction.
