But if, as the GP says, you want a program to “just let you write” (with some "writing-phase" accoutrements like change-tracking, word count, a dynamic Table of Contents, and so forth) — and you want a pleasant experience while writing, that takes advantage of the acceleration of native OS UI elements to keep that writing as smooth and jank-free as possible... then I’d assume Pages would be the clear winner, no?
(That, or just TextEdit. Though I’m not sure if TextEdit is optimized for novel-length texts the way word processors would tend to be.)