TBH, i think the series had some problems from the very beginning, but the comparatively smaller scale of events hid them well. That and the first arcs were just plain enjoyable, and the pros vastly outweighted the cons. As the story progressed those problems only got more grating and transparent, and yeah just plain worse. A snowball effect, if you will.
I still remember when Nakaba introduced PL and i just let out the biggest internal and external groan. Like why would you even do that. Who needs that. Especially when the main group is more focused on cool hax powers (or at least it used to be, back then) which can't be easily measured unlike, i dunno, powerpunching.
I dare you to give me a single instance in NNT when those funky categories in PLs actually mattered and the PL overall served a good narrative purpose except for being a lazy exposition tool (like instead of thinking of more cool powers and their clever usage we get "this is The Dude. He got PL of 70 000, so, um, therefore He Strong, and so He Punch Hard, and He Fast, good luck")
I swear to god the PLs exist solely to annoy the fans and inspire heated debates on online forums.
The moment when the series got bad (but not hopeless by any means) for me was somewhere around when Mel and Escanor were playing whack-a-mole with the Ten Commandments as the moles
It's just been a slippery slope from there with a couple of rays of hope in between