Chiming in with a reply as a new player (maybe 20-30 hours total);
Surface Instability is just not fun. What it adds to the game can be boiled down to "oh, this area is just Bad For Living In" but otherwise I never think about it. The amount of discussion about this I feel is evidence enough that the mechanic is undercooked, at least. I don't dislike the worldbuilding aspect (i havent managed to get like, any of the lore in the game yet, but its clear that something is there and as such I don't like the common answer of "just turn it off", but seeing 10k+ users subscribe to the mod that just removes surface instability is telling (not to mention how many just turn it off completely.)
I don't know what the solution should be. I had a passing thought about trying to develop a mod to make it more like an ambient value that you drift towards rather than stable regions always returning you to 100% and even slightly unstable regions dropping you to 0% after long enough. So, imagine that stability on the surface goes from 100 to 70 or 80-ish. If you're in a more unstable region, your stability will drift towards the ambient stability, but not past it. So surface stability can still be "felt" without having as much of a gameplay impact (other than, I suppose, giving you less headroom during storms, and not giving you as much initial value to work with when going spelunking)
Like, I live in a relatively cold country (Sweden). It's not like you can't live somewhere where the average temperature is on the colder side. You'll just be a little colder. It being cold outside means it's cold, it doesn't mean that if I stay outside for long enough I'd hit absolute zero. It feels weird that stability works this other way where even the smallest amount will give you acute temporal poisoning over time. (The fact that it's invisible also doesn't help.)
(But as I said, I only have some 20-30 hours in the game. Maybe I have no idea how the stability works with regards to underground exploration and this idea would ruin how underground exploration works)