This is exactly what you would expect, coming from anything from AD&D or 5E, or, dunno, Savage Worlds or Tunnels & Trolls.
In PF2, the game math mandates a completely different approach. See, PF2 doesn't do "2-3 trogs is simple, 4-6 is a challenge, 7-9 is really tough, and 10+ forget about it" at all.
Let's use actual Bestiary numbers to illustrate: Warriors are level 1, Skulkers level 2 and Leaders level 3. Let's furthermore assume the party consists of four level 2 heroes. (The math is exactly the same if your monsters are levels 8, 9, and 10 and you are level 9).
Then I'd say a single Warrior is what you'd call "simple."
Two Warriors or one Warrior and one Skulker is "a challenge".
Three or four Warriors, two Skulkers, or one Leader and one Warrior is "really tough".
Combine any two of the previous encounters, and you are immediately in "really tough" territory, if not outright "forget about it".
Only "simple" encounters mean there's a real chance of not taking significant damage. As soon as you face a "challenge", chances are at least one hero will lose half his hit points, and require healing.
At such a low level, Medicine will keep pace, so that the 10 minute downtime per encounter schedule might seem workable. As you level up, you realize you're more realistically looking at 20, 30 or even 40 minutes downtime per encounter on average. (So a dozen encounters takes four or six hours, 99% spent resting). You might bring this down by focusing your party's capacity for healing. On the other hand, any party without Medicine will definitely need two or more days to wrap it up.
More importantly, you hopefully see that the space for reinforcements is next to zero. You speak of a wandering patrol of three Trogs. I'm assuming Warriors. You can't add that to any challenging fight or you'd look at a possible TPK. At the very least you would turn the game into fantasy naughty word Vietnam, because of the harrowing difficulty.
So even hours after entering the Trog caves, and half a dozen rooms cleared, you have basically no room to play the Trogs smart, or you immediately overwhelm the heroes.
You can absolutely expect them to change gears, turning to guerilla-style warfare, or protacted diplomacy or whatever. Many groups don't enjoy that, though. (I should clearly state that this isn't even discussed in Paizo's APs).
What you can't do is just keep on trucking like you were playing another game. To do that you need enemies of at the very least three levels lower (preferably more).
Or, as I've stated already, you need to transform the game by losing level to proficiency, loosening up the very very tight math.
Ergo my conclusion: the game comes set for 4E-style combat set-pieces out of the box. If you want it to support sandbox play, you need to change something.