So, Step 1: Trap DetectionI'm primarily talking about complex traps, which are generally the ones encounters are built around. Looking at the guidelines for what a trap for a level 9 standard encounter should be (level 11 complex trap), we see that it will have a stealth and disable DC of 33 (or possibly 36 – a hazard is supposed to have at least one stat at "extreme", usually either Stealth, Disable, or save DC/attack bonus, but let's ignore that for now). Let us for the moment ignore the skill gating of requiring Master proficiency to deal with a level 11 trap, because proficiency gating is naughty word of the highest order.
Assume we don't expect a trap and are in explore mode. Half the party are probably in search mode (actually in my group it's all of them except one, but let's be more general). So the two high perception characters are searching.
I'm happy with your suggestion of a +17 for a good but not focused character. +23 is pretty high even for a super-focused character. I'll take a +20 for a 'focused' character -- because that's the stat for my level 9 investigator who hasn't put feats into it, but is naturally good by class.
So, doing the math, between the two of them they have better than a 50% chance of noticing the trap without triggering it. And since you trigger the trap only if you crit fail, then they will nearly always disable it at no cost. So over half the time a full encounter will consume zero resources and provide full XP.
Step 2: Being Damaged by the Hazard
So, now for the case when they are unlucky and trigger the hazard.
At level 11, the complex hazard attacks at +24 doing 28 points damage. Let's assume it can attack 3 people every turn at full attack (or cause them to make saves). A rough look and AC and saves says they'll hit 75% of the time, so it'll do about 21 points a round, assuming no-one raises shield, has DR or anything useful (and at level 9 ... they will!) So it'll take 4 rounds before anyone needs to start any healing.
Step 3a: Disabling the Hazard
"A good complex hazard often requires disabling multiple components or otherwise interacting with the encounter in some way" so although Thievery is the prime skill, we can assume another skill is also useful. Let's say 2 thievery and one other check.
A character good at, but not specialized in Thievery might have +18 or so. It's hard to think of a reasonable party where another party member doesn't give them a +1 at least to a skill check, and hitting a +20 to assist is not hard, so with help from 2 other people (say), +20 on their roll is what I'd expect from a party that has paid minimal attention to dealing with traps. To make those 2 thievery checks will take 4-5 rounds.
That's the worst case -- a part with only minimal attention to traps against a trap requiring thievery. For them they will take maybe 5 rounds of activity to to get through the thievery checks and will take around 300 hits of damage.No-one will be in danger, but that will require a fair amount of resting afterwards. If you have an hour you can wait, no issues, but if you need to move on fast that will be very nasty
Step 3b: Beating the Hazard to a Pulp
Hazard has AC 31, hardness 20 and 80 hits. It becomes broken at half hits, so we only need to do 40 points damage to it.
I'll assume a trap can't be dazed, stunned, flanked or anything else -- this is actually uncommon, but if it can be affected by player powers, it's going to drop very fast as it's one one creature facing 8-12 stunning / dazing / etc. attacks every turn.
So my level 9 fighter has +22 attack doing 2d12+10 on their first attack, and I'd probably do a defensive move on my second, so just +17 doing 2d8+8 (yeah, not very optimal ...) -- let's ignore the second attack. So his attack has a 10% chance of a critical for 46-20 = 26 damage and 40% chance of averaging 3.8 damage so averaging about 4 damage a round. If everyone has does about the same, that means 16 damage a round and it takes 3 rounds to break the trap.
Again, note that this is the zero-resources strategy with a party not combat optimized. Best case is probably having a double-strike pick fighter (like my son has at 9). Tricky to calculate the average math, but about 25% of the time he's hitting twice regularly for 30-20 = 10 damage, =10% of the time one attack crits and one misses for 46-20 = 26 damage. 10% of the time one attack hits and one cries and he one-shots the trap. About 10 damage a round.
So assuming you have one actually competent fighter (or monk -- basically anyone who can combine attacks to defeat hardness) your party will do effectively about 10 + 4 + 4 +4 damage a round and defeat it in 2 rounds.
Again, this assumes you don't want to expend resources and that the trap is immune to pretty much everything. So in this case you'll take 2 rounds of damage and so about 120 points of damage across the party, which is easily handleable.
- About half the time you'll detect the trap and then can leisurely defeat it. If you have a hero point to negate a critical fail, it's 99% safe, otherwise there's about a 10% chance you may enter combat
- If you only have one thievery person, and they are only "ok", not great, and the trap requires multiple Thievery checks, then you are best just beating it to a pulp, otherwise disable
- You'll never be in any danger, but it will deal about 120 points of healing on average
Is this actually true?
The above is all theoretical, but I've played quite a lot of PF2 and it matches my experience. A trap or hazard that was solo and not part of a scene was only once an issue (Age of Ashes, one of the towers in the forest) and I'm pretty sure that was not built with regular rules. We generally run a high-perception party so maybe ⅓ of the time we triggered a trap. Of those some of them we simply withdrew and slowly killed from range (this works surprisingly often -- traps are programmed so really easy to exploit) and others we usually disabled (we've always had 2+ good thievery people between rogues, monks, investigators, swashbucklers and dex fighters). We did beat a couple up, which worked fine, but was pretty boring. Once we started a second encounter on purpose and dragged those people into the trap.
Find the fun!
Solo traps are only fun if they have lasting effects that go beyond the encounter. If they just do damage, they can't do enough to threaten a party who can rest 20 minutes afterwards, and even for that situation, it just consumes a few healing resources.
However, as party of an encounter, they are way, way more fun (as @JmanTheDM says -- I totally agree) Playing an investigator, a common turn was "make a plan -- ah, a 4. I guess attacking is not great, let me disable the arrow trap!" and in general trap increase options and decisions, making combat more fun.
Even at high levels, they are still fun. Last night we decided we hated the range 1000' True Sight + See Invisible Archery hazards so much we used a wish to teleport our 16 adamantine golems off to attack them so we didn't have to deal with them. Our first attempt to sneak up and disable them went poorly and we didn't want to fight the ghost army, the flesh-warped artillery and the death knight regiment while taking 50 hit point damage arrows each round ...