I do believe a vast majority of the "classes/shouldn't that shouldn't exist" can exist simply by being descended from those who arrived when the island was still chartered on maps. And those that can't, like classes such as Firebird, can be flavored in a different manner. Dev has given us /something/ of a timeframe by barring Zerans.
Also, handwaving exists for a reason. Buckle up your pants and stop worrying that Jimmy Glykin Kensei is going to ruin your immersion. As much as I would like to walk up to Dev and say "explain this, this, and this about Korvara", we're still sitting in the dark and we don't need to get in a twist regarding lore. In the end, people are just trying to have fun, which takes importance over trivial things like why certain classes shouldn't exist.
For a game that lacks diversity due to its combat system, we shouldn't trim it even more.
Also, handwaving exists for a reason. Buckle up your pants and stop worrying that Jimmy Glykin Kensei is going to ruin your immersion. As much as I would like to walk up to Dev and say "explain this, this, and this about Korvara", we're still sitting in the dark and we don't need to get in a twist regarding lore. In the end, people are just trying to have fun, which takes importance over trivial things like why certain classes shouldn't exist.
For a game that lacks diversity due to its combat system, we shouldn't trim it even more.