Vitality and endurance.

I don't think they should make them less useful but in Demons, there was a reason you had two ring slots, because each ring did a single effect, rings had to compliment each other. There should be plenty of rings but with reasons to hold on to them. Like for a ring that steals HP at a low-static rate, allow me to scale it to some extent, just like no armor is really obsolete because you can level them, a similar mechanic for rings with a single function.

I'm actually for the idea of an neck slot and have that be for things like basic-needs-boosting.
You could equip anything from capes and scarfs to necklaces and amulets.

the only ring that i can think that as more than 1 effect is the FaP

So obsolete it with better scaling. Need more useful, scale-able, and complimentary functions. So the same few rings aren't used by everyone, variety to cater to different builds.