like a reddit thread talking about being able to do 520 damage in one attack, some chatter about a "resentment witch" being able to make power word stun or color spray effectively permanent, and a youtube video by the rules lawyer about "OP builds", so it seems like there's at least some system exploitation going on.

Surprisingly, as OP as they seem, they're entirely in line with the intent of PF2e. 520 damage might seem like a lot, but it takes a specific enemy type, some prebuffing, 4 actions (plus any necessary movement) to prepare, 4 spells from 3 other characters, 2 more actions to execute the attack, and some incredibly lucky rolling - an equal level wizard can just use 2 actions to cast the 10th rank spell Cataclysm, and with similar dice luck deal 420 damage. 480 if the target is swimming. That's just level 20 PF2e.
Similarly, the resentment witch is just meant to make those conditions permanent - enemies of a higher level than the party have their success level against those saves increased, so while they can be a huge boon, they're unlikely to do much against enemies they'd really turn the fight against - being able to extend what effects they can land makes incapacitation spells worth potentially wasting on bosses, with the high chance of the spell doing nothing and the ability not even coming into play being the trade off for the power of the ability. Even if the spell does land, it'll be a lesser version of the effect that is extended.
I don't watch the rules lawyer, but from his interaction with the PF2e subreddit I'm pretty confident it's a clickbait title - they'll be powerful builds, but entirely within the intentions of the system, and ultimately as useful in game as most other builds.