And what is the logic for the 'classic' D&D save categories? There's no rhyme or reason to it whatsoever. The whole thing is utterly arbitrary and each category is used virtually at random for different things, lol. At least with FORT/REF/WILL defenses there's some logic to what each save represents and why your PC has a better or worse defense in that category.
At random? It's pretty specific actually. In fact, the problem with early saves is it might be TOO specific. So, this whole "random" argument is entirely BS.
And, what you're missing is that Fort / Ref / Will doesn't account for @DMKastmaria arguments at all.
The main benefit of earlier saves is that it WASN'T unified. So, the Thief could have just as good of a Save vs. Poison as the Fighter.
Why? Because the Thief is good at dodging poison attacks. The Fighter on the other hand is just plain tougher.
In the F/R/W crap, we have to deal with the Thief who SUCKS at Poison saves because it's all rooted in Con and can't take into account anything else. And, the Fighter who BLOWS at Will saves because it only takes into account his Charisma or Wisdom or whatever. With the old school saves, a Fighter could use the same saving throw and be good at it for different reasons. So, each class can be taken on its own merits and tied to save numbers that make sense for that class.
There are benefits and downsides to each.
But, to try and claim F/R/W is inherently better is just bogus. You seem to do this a lot.