darjr
I crit!
I like the idea as far as making multiclass characters effective but in story terms I'm not sure how it would work out. Should a 15th level fighter who takes a single level in wizard be a better spell caster than a 1st level wizard, or even a 5th level wizard because of their character level. The same goes for a spell caster crossing into fighter. Should their martial damage output be based on character level.
To be honest it has always been the martial/spell caster mix that has always been problematic but as RangerWickett points out this may no longer be a big issue
good point. Though the class level limit about what abilities they could take would solve some of that. And the flatter math also means that the 'bump' doesn't have to be as drastic as it would otherwise be.
In story terms I'd liken it to a more experienced person being better able to learn new things and use those new things more effectively. Especially up at 15th level or so.