Mixing and matching units and classes is an expirence, sometimes when a unit's stat spread and a class's stat spread don't line up it creates a wonderful versetile unit with a well rounded stat spread who can do anything... and sometimes it creates whatever this is, a unit who clicks terribly with the class and just doesn't function

In this case Charlotte's speed gets dragged down and instead of a fast General we get a slow Charlotte, and instead of General bringing up her bulk to passable levels she's still too frail to sweep without outlandish help, the only stat that ends up passable is her strength but it's not as good as it would be if she just stayed in Berserker, truly just a trainwreck unit

At least you can fix anything with Corrin pair up