Does that apply to dungons in PF1 adventure paths as well? Is the 15 or so combat encounters in the Thistletop dungeon in RotRL, for example, a TPK waiting to happen? Do I need to substantially reduce the number of encounters in dungeons when I convert RotRL to PF2?
I would read thru the dungeon and see if there are any logical 10m break locations so you can use moderate encounters leading to a severe boss. Anywhere it does not make sense to break, then add up sequential encounter XP ... if it comes up to severe or extreme and you still do not have logical breaks then step down the encounter difficulty. You do not want every encounter being a multiple critting boss level of difficulty, instead you want to wear them down - which is what low and trivial encounters are for. Port the encounter idea into low/trivials, do not port the exact numbers/creatures. Another option is wait for gamemastery level removal rules, which will widen the +/-4 threat range and reduce boss threat levels (at the cost of increased minion power)
Plaguestone was written with serial dungeons of excessive difficulty. The first one had winding chambers that gave 10m isolation between rooms. Most of the others are written that the subsequent encounter is not going to aggro into the first otherwise they are meant to combine into totaling up to a severe. The NPC are laying in wait for PCs or preoccupied with their tasks and will not cross rooms. The worst part is the orc fort which as designed ends up as a beyond deadly yard fight with a sniper - it requires creative play to solve that (PC snipers)
Play experience so far has been the encounter difficulties are dead on. Unless they find a creative bypass (like feeding the snarling wolves and turning them into friendly puppers) severe does indeed mean go all after resting then need to go back to camp level of difficulty - and if camp is unsafe from randoms then they need to get back to town. If you insist on 10m break only every two moderates - there is very high risk players will not survive the level.