Taco, the point is not that you have to have these classes to run GHA, this is just what some think is optimal. I think the tank and healer are the necessary ones. The other 3 are a little more flexible.

I do think you should be shooting for one of these builds though for your character for GHA and future dungeons. Great thing about AA is you can just level your other classes.

Make sure you save all your xp generating tasks and do them under a vocation pot for double xp. I always save up enough items that will take me the full hour to do at once and drink a pot right before.