Ok, I thought PF2 changed that from 3e/ PF1.
Well, don't take my word for it; I've read the encounter building guidelines, but since I'm not GMing they aren't likely to have stuck perfectly, and since I did run 3e many years ago, I may have conflated them.
Yes. The more levels the more gradual the progression can be. So yes, I feel we need at least 20 levels, maybe go back to the 36 levels of BECMI!
I'm guessing from the way you've phrased this that what you mean is that you can have progression be visible but minor (since, after all, you can have very gradual progression with ten levels--it just means you'd spend a long time at any given level).
I at least understand your position now; its not something I'd go to a level based system for at all, but when in the D&D sphere, that's what you're dealing with.
We play the whole range, so I feel we need it all. I guess we could cram it all into 10 levels, but then you get to much at each level, and that is not what I want.
I might have confused you with someone else I've been talking to; someone indicated they usually bailed after 12 levels.