1. There is a slight performance gain when you're dealing with more than 3-4 subroutines

That sounds like something that would have to happen in XS.

2. Debugging is much clearer because your callstack only has the subroutine called by the client and not all the intermediate subroutines.

Sub::Uplevel could be used, but that adds overhead instead of subtracting it. (There's also an off-by-one bug in it; I sent a patch to Schwern several months ago but it seems to be way low on his tuit list.)