I use gradient masks a fair amount in my tools, or as AFB says above, I also use literal grad filters (rarely). Outside of iPhone-only photographers, not sure how many people on this forum use Apple Photos, to be honest, which is maybe why you aren’t getting the responses you feel you should be. I know a goodish number of us are using other tools that already have that feature. It’d be nice in Photos, for sure, don’t get me wrong, but I don’t see it happening soon. Masking and localized changes aren’t anything Apple have even hinted at wanting to take on, as far as I know. Once Aperture went away, I went elsewhere for photography software.