All those early CCed units are broken, and there's no way to "fix" them. That said, while they will suffer lower stats, it's not entirely the end of the world, in most cases, you'll just have to level them higher than you need to for the same content. Some of those units are very good and can still be used despite the lower stats (although a painful sight nevertheless).

Sophie and Marr should still be usable despite the marginal stat loss (compared to their max stats). Neither are really replaceable regardless.

Despara and Gellius almost drops a tier due to the missing stats (and higher natural cost) and should only be used if you don't have anything better to replace them (getting a mincost Belinda in the current revival would be ideal). Once you get a better replacement, you'll have to do some research into SAW and decide for yourself if they are worth keeping or to sell them off for rainbow crystals to get Danchou.

Saki and Mehlis are replaceable, so there's no real worry there...

Dahlia isn't really a highly prized unit, so while it's a waste of a -2cr plat valk, you can keep her around as a valk buffer or something.