D&D 5E Count of 5e saves from MM and PHB by stat and class

I dunno if it's really fair to weigh saves against one another, even if you start doing things like taking into account effects of failed saves. I think it's also important to see how the six stats influence ability checks and factor that into usefulness as well. So sure, STR saves are common (though the effects often not terrible) but STR is only tied to one skill. CON saves are common and can be pretty bad as well, but CON isn't connected to anything else except hitpoints and concentration. INT and CHA saves are rare, but there are lots of skills that use both. So, while the saves for these are rare (but nasty if failed), they're very useful stats generally because of how many skills they're connected to. If anything I'd say WIS and DEX are the most disproportionate ones, since the saves are common, moderately nasty if failed, and the skills are linked to things that are universally beneficial like AC, initiative, stealth, perception, etc.

Yeah, that sort of thing is really tricky to balance. Sure, Str is only tied to one skill, but, depending on the campaign, that can be a REALLY useful skill to have. Tomb of Annihilation was mentioned, where you have all sorts of exploration. I'd presume that Athletics checks would be pretty common - climbing, swimming, that sort of thing.

It's really hard to claim how useful one skill or another is. It's so campaign dependent.