I'm not sure how much of this can be affected by mods, but in this mod bastions and capital ships seem to be pretty dominating forces - one star destroyer is more than capable of tanking and destroying vast fleets of corvettes, and bastions are practically impregnable with starting game fleets that aren't totally concentrated and bulked up. The AI, however, still seems to be working closer in accordance to base Stellaris rules and will happily hurl their fleets at bastions, lose the lot, and then rebuild with the cheap corvettes they can afford instead of saving up and investing in the big ships that make a true difference. The result is that even if the AI is theoretically even to you, they screw themselves over very quickly and become little challenge. Is anyone else seeing this, or is that just me?