Your idea about -Q inhibiting native comp was obviously not implemented.

In my setup, I call `startup-redirect-eln-cache' in init.el because I don't
want the cache in my .emacs.d/.

However, when I'm using -Q to test something, I do
M-x whatever-which-loads-a-module and end up getting an unwanted
.emacs.d/eln-cache/

So either a --no-native flag (setting
`inhibit-automatic-native-compilation',
and perhaps `load-no-native', to t) or having such behavior in -Q would be
quite helpful.

Yes, I can define an alias to use

--eval "(setq inhibit-automatic-native-compilation t)"

I already have. Still, I regularly forget it and default to emacs -Q.

So, FWIW, I agree with your sentiment that -Q has no single defining goal
other than "do not do unnecessary things, please", and inhibiting native
comp would fit quite well.