Optimized high level combat is pretty much just a coin flip to see who goes first.

It is frighteningly easy to execute an OTK in the current environment. Buff myself with a high amount of loaded roll and advantage to increase both hits and crits, stun the opponent just for the massive damage bonus, then spend the rest of my AP throwing out 10d6+DMG. This results in multiple crits, some of which even get over 200 dmg.

Personally, I would just scrap AP entirely to facilitate actual proper back-and-forth gameplay, perhaps replace it with an Agility stat that determines who goes first and can result in extra turns if it's significantly higher than the opponent.

If that doesn't sound good, perhaps something similar to multiple attack penalty from Pathfinder Second edition where you get a stacking to hit penalty on subsequent attacks, perhaps penalizing repeat moves and maybe forcing diversification.