I don't think the expanded ability list is slowing down combat, at least in the Goblin camp.
There you just wait for the AI to figure out a way to get you for ages (particularly if you have the high ground) and then make basic attacks. That is slow regardless if you revert to basic 5e rules.
Optimizing the AI decision making will speed up the game significantly and I think that is really the only solution here.
How that is done is up to the devs.
