Make the AI more cautious in attacking, basically it shouldn't attack unless it has a clear advantage (let's say 60% win chance). That said I've seen the AI actually not attack the first turn they laid siege in my current campaign, maybe it was a fluke, maybe my changes were on the right path, we'll see.

AI doesn't protect its naval transports enough and sends full stacks with little protection, this is weirdly more salient in RotS. The trade ship fix might have helped with that.

Minors should use their navies more defensively. This will probably make the naval game a bit easier, but currently they're just causing headaches while leaving their ports undefended.

If you have any additional feedback, or ideas about how to fix this issues, let me know.