i pretty much agree with you on rules in that they should be functional enough to play the game as intended out of the box with no or minimal tweaking, because otherwise why the hell am i buying them. i'm perfectly fine with tweaking rules to support how a setting or campaign works, but i think most people are fine with that so it probably doesn't mean much.
i actually think the rules are EXTREMELY important to the experience. they do a lot in establishing how the game world feels. just as an easy example that i'm sure you'll recognize, adding half your level to everything makes 4e feel much, MUCH different from 5e - 4e feels much more like the party are mythical heroes ascending into legend by fighting what should be invincible foes, while 5e...i mean, the foes can definitely be threatening, but i don't really think there are many monsters in 5e that couldn't be defeated by a large, prepared army. and even 4e feels different from pf2e in that regard because of how each game handles crits. in 4e, even that seemingly invincible foe could theoretically be destroyed by an army of regular soldiers if they were careless enough to get crit a million times. in pf2e? hell no, that monster is LITERALLY invincible to those people, they literally cannot even deal damage to it. and that's just one aspect of each game.