Well, it depends on whether or not "4-5 years in related experience" means systems programming or if it means making single-page webapps.

That's less than somebody with 0 years experience in FAANG will make. I wouldn't expect kernel developers to get paid much differently than non-kernel developers at a similar level.

FAANG rates aren't normal outside of FAANG (and maybe finance).

What if it's systems programming or HW design?

It's really just down to location, then. They vary so much, and I don't have a lot of experience in the locations you mentioned. You can expect high-end software engineering salaries for good kernel hackers.