Multiclassing and Extra Attack

So I'm always a little annoyed at how well full casters can multiclass together without interrupting their spell slot progression, but I've come to the conclusion that my rage is misplaced. It isn't that I think a 2Sor/2Bar/1Cle shouldn't have third level spell slots, it's that I think a 2Fig/2Bar/1Pal should have extra attack, that 4Mon/3Rog should have evasion. Multiclass levels that are empty because you already have that feature just feel bad, and this seems like a simple solution.

Has anybody played with a homebrew at all like this? Does it work at all?