This is what irritates me about Parental Controls in 27. Everyone has to be on 27 or nobody gets the new controls. So, we still have a mini 5 that we let the littlest one on. It works, there's not reason to get a new one, but sure would be nice to have the newer Parental Controls for the older kids.
Disclosure: I work at Apple. But that’s also my honest opinion.
Part of Apple's whole appeal is that you get OS patches for a really long time. Outside of tech enthusiast circles, it's not that common to YOLO into bleeding-edge OS updates
Anyway, I'm not criticizing. Run what you like! I just don't expect the overlap between "buys Apple device in entirely new category" and "running OS version from two years ago" to be very large.