OK, so here's what I know.
I came into contact with a few max level characters along the way, so I decided to ask some of them what they knew about the class. Very few of them have played on JP servers before, but I did ask what I could.
One of these responses were "It makes damage-focused class builds look like a joke".
If they're really THAT overpowered, then I fear for the current state of balance in the game for the Western servers. IMO, Hero and Phantom should be either Nerfed, stay Removed, or Restricted more than it is already.
Speaking of Restrictions tho, I did get info that it requires you to have 2 classes at level 75 before you can use them. HOWEVER, I feel that this is still too easy to accomplish, as I have 2 level 50+ characters already and it hasn't even been a week since I started.
I know some people are going to complain and try to argue along the lines of "but I like being overpowered, don't nerf". But IMO, if said classes are even gonna be added to the game, then I rather raise the requirements to unlock such an overpowered class. If anything, ALL 9 original classes should be lv75 (if not max level) before you should be allowed to wield such power. If you want to be overpowered like so, then it shouldn't be something that can just be accomplished within just a month. "Work hard to Play hard" as some may say.
These are only my thoughts, in the case the mentioned classes are as overpowered as people say they are. I have no experience on either class, and I only go by what I've heard from others.
I've seen people on the field do 10,000+ damage per hit before, but if that's gonna be a "joke" compared to what Hero and Phantom can do, then it really worries me if such a thing exists in the game.