They still support the LaTeX command set, except they're native Unicode and native OpenType support. That's kind of where the full stop should be satisfactory. If you need to typeset anything, having the LaTeX commands _and_ normal text typesetting for arbitrary languages is literally why base LaTeX with pdftex is now effectively irrelevant.
If you need amsmaths or APA citation, you still get those. Except now you get them without insane commands just to type Paul Erdös' name, or citing Лев Семёнович Вы́готский.