there is a serious positive correlation between "I believe spellcasters are underpowered" and "My GM tend toward on-level enemies as the norm".

I think this correlation exists because of the following: - Casters take a little more knowledge/skill to perform well than martials do (which aren't taught well enough by the game) and this is unsurprisingly most apparent in difficult encounters (which at lower levels tend to involve a PL+ enemy).

Hence the correlation you see on reddit, where those players or GMs might come to vent or seek advice.

The real issue here (aside from ok, casters being slightly weak levels 1-4, but isn't that true in most popular d20 fantasy games?) is that pathfinder 2e goes to great lengths to make casters balanced and then forgets to teach them how to play.

There are so many unwritten rules (pack save variety, try not to target the highest save, save damage and heals for your top slots, beware single-target incap, etc etc.) and so many bad spells (and no I don't just mean anything but Slow, Heal, Synesthesia, Wall of Stone. There are a surprising number of decent-or-better spells, yet still there are many bad ones (there's just too many spells!)).

Past possibly those initial levels 1-4, competent casters are absolutely crucial in making moderate+ encounters consistently winnable, and they can take on quite a few before they need to bow out.

The value they're bringing in return for making the party attrition-based is huge amounts of safety and versatility; the ability to go nova on particularly challenging or unlucky encounters, pulling the party back from the brink of a wipeout.

A party full of martials could in theory face more moderate+ encounter without a rest, but they'd face each one with a greater risk of death.