I’m grouping these together because I think they’re getting at the same underlying issue: different groups have different levels of expertise (tactical acumen, char ops, etc), which affects the overall balance of the system — or perception thereof. I agree a system needs an intended audience. Even if you choose not to have a one, you’ll still end up designing one for an implicit audience.
Completely agree, though I think many RPGs (including specifically the D&D line from day one) have tended to be in denial about this.
I think it would behoove Paizo to recognize that the mathematical underpinnings of PF2 gives it the flexibility to work with multiple groups. What I mean is explicitly calling out that the default assumes a decent level of tactical play. If your group is less interested in or just not good at that, then you downshift the difficulty. If your group is really good at that stuff, then you can upshift to even harder ones.
I have a vague memory of some reference to doing this, but I could be conflating things from other games.
In a sense, that’s what people are doing to make PF1 (and other games) “work”, but PF2 offers a structure that can scale up or down. From what I’ve seen, I think it would be enough to make the default moderate-threat encounters and suggest that groups that are bad at tactics can use low-threat ones as their staple encounters and really good groups can use severe-threat ones.
The problem with doing this with PF1 and its precedents (and its cousin D&D 5e) is that, bluntly, it wasn't very well balanced internally; rather than just balancing encounter levels or the like, you had to juggle a lot of individual things based on the specifics of the player (and character) group. PF2e isn't, of course, perfect in this regard as when you start to approach perfect balance there are some knock-on effects that some people find very distasteful; D&D 4e probably approached it closer, and you can see the, shall we say, widely varied responses to that (it was, I think, on the whole a bridge too far for me, though I'm not actively hostile to it the way many people were). PF2e is a compromise here where there's still a little wobble in the structure, but where the degenerate cases tend to be fairly fringe, whereas they could be in (for example) D&D 3e all too common.
You're correct that its much easier to do this sort of adjustment systematically in PF2e.
The benefit of making this an explicitly tunable knob is it helps groups that don’t realize you can turn it, and it should help normalize different levels of play in the community. One could argue this will just create opportunities for toxic people to crap on people who prefer the lower difficulty, but those people already exist, and they’re doing it anyway.
You do also have the unavoidable problem that groups are often not evenly skilled/interested internally. This is obvious in anecdotes one hears where one group is groaning about that one guy that always goes off half-cocked, or another group that rolls their eyes about the guy who always second guesses what they do in a battle. These are clear cases of the one-man-out who is not in sync with the rest of the group, but its not uncommon to see some sometimes serious variation among a group, which can make setting such things complicated.
But that's a problem no matter how you go about it. It can be very hard to properly construct a combat when, in practice, approaches within the group vary radically.
Official adventures present a problem, but if the difficulty knob is now an assumption, then they could include guidance like they do for adjusting for party size. I’m not sure whether that would be in the CRB or the adventure because I’m not sure how party size is handled now. I’d expect the guidance on difficulty tuning would work similarly to how they do party size today.
Generally speaking, party size modifies the expected experience budget you're supposed to use when constructing encounters (with the careful note that its usually better with larger groups to increase numbers of opponents than quality).