Now to address whether a system that has more AP could easily take the place of the 3AP system.
Yes of course. Really all it is, is numbers. What the 3AP system introduced that needed to be addressed was AP inflation, Limiting the number of actions in a turn, as well transforming AP cost into how useful the skill is on the battlefield (and Nothing else!), And to boot putting the enemy and the player on a similar playing field without destroying the action economy.
Don't get me wrong, low cost but highly effective skills have their place. Heck 0ap skills are essentially class features you activate (and often essential to using that character).
Heck I was open to the idea that someone could get a talent or ability to later have 4ap a round. Yet ultimately the amount of AP the player should have access to NEEDS to be constrained.
- attack up to 5 times per round
- cast up to 3 cheap spells per round (mind the cooldowns, though)
This is basically the opposite of what I want. Especially since the game itself couldn't handle enemies with as fruitful turns as you have, often needing to kite enemies as a full attack turn could kill you in one hit.