Yea they aren't simple, path finding is actually a crazy expensive operation in general and as far as I know stellaris isn't using an optimized version that does bidirectional search. (People say that lgates and other shortcuts slow down pathing which is only true in single directional search not bi directional).
Stellaris ups the cost a lot because if you can fly through an area or not isn't actually fixed and changes regularly. So a cache for a specific path breaks often.
Ship trade upkeep cost calc is negligible the game already has a bunch of expensive upkeep cost modifications based on ship location. The AI has DRAMATICALLY more ships in endgame right now then it did in 3.14. This isn't really from economic changes as much as the game actually tells the AI to scale naval capacity ALOT sooner then it did in 3.14 in 3.14 it basically only happened when they had repeatables.
That doesn't just scale pathing cost but every single war decision has to loop through all those fleets. Just having more of the scaling like bioships do where we get larger versions of ships would cut down on that alone. Cutting down on the number of small ships like corvettes to be 0 at endgame is going to do far more then anything else TBH.
