Such a neat concept! Incremental and RPG seems like an amazing combo. The RPG dungeon aspect makes the idea pretty clear. Also bottlenecks are much easier to spot than just incremental math due to the combat! It also have the appeal of RPGs with getting more powerful.
One note on the progression - locking the mage behind the speed update could get people stuck - since you are not really bottlenecked for speed most of the game. I took it just for completion, but I could see easily that someone might think they don't need speed and unlock the other classes much later.