A huge post. I realized my reply were become nearly as huge so I'm chopping it up.
As I read you, you are defending Paizo's decisions to lock in the exact improvements in a class' fundamental bonuses (to hit, AC, saves).
Not so much defending it as understanding it- in a class-based system there have to be distinctions. The logical question then becomes- Why make a class-based system at all? Which is a very valid question. But we're not discussing that, so class-based system it is, and it has to lock in some differences.
But then you argue the difference isn't that great anyway. Doesn't this mean you're on my side - there was no reason to lock it down, there was no reason to deny the player the satisfaction of making his or her own choices?
Didn't say that- or at least I didn't mean to say it. The differences are really big. REALLY big.
At any given level if a fighter is getting hit 65% of the time (hit on 8+, which seems pretty common) while another one is using a steel shield and raising it, the one raising the shield is taking 25% less damage. That's just for having +2AC and before we even talk about using the shield to block incoming damage. That's... a pretty significant improvement for just adding 2AC.
Giving a character a choice is always good, as long as the choice is genuine- there's no genuine choice between +1 to attack and +2 to athletics and acrobatics (two actual feats in PF1), there was a choice which made your character substantially stronger and one that didn't move the needle at all. There are definitely better feats than others in PF2, but that huge disparity isn't there yet, at least not most of the time.
In 3E it is the multiclassing mechanism that provides the player control over his fundamentals. It is in this light PF2 comes across as weirdly - almost paranoiacally - locked down. There isn't even a token ability to switch around your saves (as in 5E, where you could take a feat to boost a given save, but since you have six of them, you basically chose your most important one and that was it).
There is a way- Canny acumen, which takes the pf2 equivalent of a "Poor" save and makes it a "medium" save.
There is definitely enough design space to sacrifice enough to make a save a "good" save too- it just hasn't been implemented yet.
Being able to juggle around your save proficiencies just like you're allowed to select skill proficiencies would have destroyed nothing, made the game slightly more fun, but most importantly, blunted the impression the game knows better than you, and makes the decisions for you!
Again, I think the design space is there to implement this. The issue here is how to implement it in a way that doesn't just make it an almost-automatic wisdom choice, as in 5e. The saving throws should be a clear point of distinction between classes if they're being used to balance the classes- something that appears to be the case.