CapnZapp
Legend
First we need to establish we're talking about the same thing. 5E uses "tiers" as shorthand for "what the heroes get up to" - or what sorts of challenges are appropriate. That is, tiers mean nothing more than things like "a stone wall is a significant challenge at tier I but not at tier III because there's so many ways to fly over it or teleport through it or even smash it with you fist".
So in that general sense, you can absolutely use the same thinking and the same terminology. In other words, you can say PF2 too has four tiers of play.
Of course the games aren't identical, and so a particular effect doesn't come into play at the exact same level, and in some cases you can't even do a thing the other game lets you at all. (In general, magic in 5E is more generous. At the highest levels, though, magic has arguably a greater impact in PF2)
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That said, my guess as to why PF2 doesn't talk tiers is the lack of bounded accuracy.
That is, at any given level, monsters can (and should) be of four levels lower than the heroes up to four levels higher than the characters.
So, if the heroes are level 10, only monsters of level 6-14 work well. (lower and they're completely trivial; higher and the heroes should flee)
This way, you have one "tier" at level 10, for level 10 characters, encompassing monster levels 6-14. Then you have another "tier" at level 11, encompassing monster levels 7-15. And so on, ending up with twenty tiers... or levels, as it were.
This is because any given scenario becomes significantly easier just by leveling up. Once.
If the party holds off two levels, that particular adventure is now outright simple.
This goes counter to the sandbox idea to let the heroes choose what to do (and in what order)... unless you let monsters level "dynamically" (to use a computer game term).
But if the bandit chief is always two levels higher than the party, regardless of when the heroes decide to wipe out the bandit gang, then it isn't a true sandbox.
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For your sandbox, you might want to use the proficiency without level variant of the Gamemastery Guide. If you don't you can't really have a true sandbox like one meant for heroes of, say, 5th through 10th level, since any monster that's a challenge for 10th level characters will just stomp on fifth level characters.
In a way that just doesn't happen in 5E (because of the deliberate design decision called "bounded accuracy"). In 5E, a level 5 party can totally experience the thrill of seeing a level 14 monster. Unless the DM goes out of his way to kill the party, they can survive long enough to realize they need to flee.
In PF2 a level 14 monster will simply kill one character each round without breaking a sweat. Such a thing is no fun.
So you can't just have the level 5 party randomize encounter the level 14 monster, which is what a sandbox is all about. As soon as you try to solve this, it's no longer a true sandbox, whether you place hints so the party knows what to avoid, or simply create two or three areas, so there's no monster more than 5 levels higher than the heroes at least. (Even facing a level 10 monster - any level 10 monster - is a nasty experience for even the most minmaxed level 5 PF2 party...)
So yeah, that's my response to the question of tiers.
