For one, there is no "Model Mega Man". There is Models X, Z, H, F, L, P, W, O, and A. They are not just "reused" Zero characters, each one is remarkably different than the Reploids their Biometals were based off of.
Vent/Aile do not have the insecurities of X.
Giro is not cold, unlike Zero.
Aeolus is an asshole, Harpuia wasn't quite as bad.
Atlas believes war sparks evolution, while Fefnir just wanted to blow shit up for the hell of it.
Thetis is whiny, Leviathan is just agressive and just a little bit of a bitch.
Siarnaq literally has no personality whatsoever, while Phantom was decidedly honorable and, well, had a personality.
Serpent did not want to destroy the world, while Dr. Weil did.
Model O had no set Biomatch, even though it was apparently going to be in ZXA. But Omega just wanted to kill shit and had an inferiority complex; any potential Biomatch for Model O would be a bit different.
Grey/Ashe did not have the hero complex that Axl did, and Model A, despite its apparent name, is NOT based on Albert, functionality-wise.
So yeah, there weren't any "reused Zero characters" in the ZX series. Considering what a Mega Man is, by definition, in the ZX series, all of them should be considered Mega Men.