Also, are you proposing that low power mode with wifi uses the same amount of power as lower power mode without wifi? If I know I'm not going to see a power point for many hours, I turn my phone onto low power mode and turn wifi off (and the brightness right down and some other things). I might do it as I leave the house in the morning when I still have 95% battery. In these cases, I very often need my phone most in precisely when the battery will be weakest.
Having had this discussion a few times, I'd love to do a solid battery life investigation of turning off wi-fi properly versus this toggle.. given it disables auto-join I imagine the scanning frequency is significantly reduced and thus the power usage is probably relatively comparable (close enough). But that's just a guess, I don't know for sure, but I'd sure love to know.
I'd also love to know the battery impact of turning bluetooth off entirely. These things all seem like antipatterns to do as a regular usage thing and I think that, in most cases without actual research, they're a bad idea for people to get into the habbit of. For precisely the reasons outlined here and by apple.. later using mobile data accidentally, being confused your apple pencil works, etc.