@Siegfried: Sounds like you haven't played Shadow Dragon or NMotE in a long time. In these games, what classes a unit can reclass depends on the class set they belong to, which depends on their default class. These are the sets:
1) Mercenary, Pirate, Fighter, Dark Mage, Knight, Cavalier, Hunter.
2) Myrmidon, Archer, Cavalier, Mage, Cleric, Dragonknight (after promotion)
3) For women: Same as 2, but change Cavalier for Pegasus Knight. In NMotE, women can become Cavalier and after promotion Generals and Paladins.
My avatar's default class is Mercenary, now Hero. So my only reclass options are General, Horseman, Berserker, Warrior, and Sorcerer.
Changing him into a Berserker or Warrior leaves him still OP. Changing him into Sorcerer leaves him useless. Into Horseman and he would be even more OP. Into General and he would become truly unkillable.
Sure, you can unlock the other class sets for everyone after finishing the game in Hard Mode, but I haven't done that yet.
Also, Myrmidon isn't a starting option for Male Avatars, only female ones. I did make a Female Myrmidon in another playthrough. Result: The same.