An important note that is often missed by those talking about Dexterity saves as being top priority is that it isn't just how frequently a particular ability score is used for saving throws that matters, but also the severity of the consequence for failing the saving throw.
As a result, Dexterity might be the most commonly occurring, but it isn't the most punishing upon failure because typically the difference on a fail is taking more damage than you would on a success.
Constitution, Wisdom, and Charisma saves all have more dire consequences upon failed saves, things that take your character out of action for some period of time or actually impair your ability to do things, and thus should be considered at least equal in importance to Dexterity.
So...a save that shows up in 8 out of 482 (based on Kryx's numbers, with much thanks!) abilities/spells is so massively important that it balances out, y'know, the save that can do just as bad of things to you if not worse (Mummy Rot, Contagion), or that are utterly crippling to many characters (Poisoned is almost always gated by a single Con save, and imposes disadvantage on
all attack rolls and ability checks)? I'm sorry, I'm not at all convinced. Particularly when the really serious spell that uses an Int save--Feeblemind--is an 8th level thing, and the next-most-serious (Symbol: Insanity) is 7th level. Phantasmal Force, the only other PHB spell that uses an Int save, is not nearly so dangerous as you describe. It looks like the remaining 5 things are MM/EE/DMG/etc. stuff, so I don't know about them--but I find it highly unlikely that they're as serious as you allege.
Con and Wis are clearly the best saves for avoiding dangerous status effects. Con and Dex are the best saves for reducing damage. Combined, Str/Int/Cha account for only 108 of the 482 possible saves--and (nearly) three-quarters of
those are Str saves. So...yeah. Dexterity probably isn't the
absolute best save, but it's certainly a nice one to have, and the second-most-common save by a good margin. It's also the only save, at least AFAIK, that gets features to make both successful
and failed saves better (Evasion).
Constitution is the best save by a long shot--not only because of the sheer number of terrible conditions that hang off it, but also because it governs Concentration. But I think it's pretty much inarguable that Con > Int or Cha in the vast majority of situations.
I also find it humorous that the Dex save is apparently not that great because it "just" halves incoming damage, but stuff like the Bear totem features of Barbarians are crazy awesome...because they grant resistance to damage, which
just halves it.