Note that LaTeX2e is just a set of commands, a bunch of which are absolutely ridiculous to use in plain LaTeX, and simply not used when using LaTeX in conjunction with XeTeX as engine, because XeTeX can do things that plain TeX just can't, and so all the insanity that LaTeX2 had to invent to make TeX "do things it was never designed for" simply aren't used when you're writing XeLaTeX documents. Like everything being Unicode by default, no packages/macros/special affordances required. Including not needing stuff like \hat{...} or \grave{...} because those make no sense when everything's Unicode: just write text. Or having direct font access instead of needing to go through the horrendously outdated TeX font metric concept.