As a programmer, there's a lot you can do to make your JS run faster under optimization (e.g. avoid deopt) but there's little you can do about the warm up (besides reducing binary size).
So, when you're trying to progressively improve performance of specific code (e.g. boost FPS) the warm up time is better ignored; it's not under your control.
Reducing size or switching to WASM are both things that you can do.
You should measure the cases you actually care about. For a long running app, start-up time is probably not the most important thing, for other apps its very important.
So, when you're trying to progressively improve performance of specific code (e.g. boost FPS) the warm up time is better ignored; it's not under your control.