Emacs has some design decisions that are the result of 20 years of concessions on a ton of different platforms, and some of those are questionable anno 2017.
Emacs' actual codebase definitely isn't bad.
To clarify: I'm not saying that locally the code is bad, I'm more talking about the kind of macro issues outlined in Buttery Smooth Emacs. But it's these kind of things that will be harder to "fix" in a port.
