I just had a thought:

Why not make it so that changes to skills that are OP when used with subclassing but fine without, apply only when subclassing, so using skill lines from other classes?

That way subclassed characters can be balanced the way the devs feel is neccessary without having to inevitably downgrade pure classes.

Not sure if this was brought up and I didn't think it through a ton, just a spontaneous thought I wanted to share.