why can ha and aa still switch from def to att and la can't?
what do you mean
They have enough vit to switch with just vit stones but la classes don't cause they need 620 for def gear
No they do not have enough Vit. How? Well, you are considering the vit provided by shards from gears (80Vit from 4 shards on each gear).
The def set for HA requires 540 base Vit to equip and 740 for defense cape. Means we do not get those vit points from gears since we cannot equip them. So, only Barbs can efficiently use the defense set. Even if a BM puts in enough pts into vit AND uses a vit tome, he will still not be able to assign enough pts into dex and str to be able to use Axe and Fists without pts reset.