As soon as Hendrikson was defeated. Nothing later in the manga compares to his arc. The 10C's appearance wasn't especially amazing, Galand's entrance was bad, fodderizing everyone pointlessly made it a requirement for every single person to power up, and the introduction of PL's was the biggest mistake Nakaba has made imo.
Other than that, Mael vs King and co, the Zeldris' fights, the Sinner, and all the 10C fights were all around the same quality. The only standout moments were Mel vs Escanor and Purgatory, which were pretty good, and then there was DK Mel getting his ass handed to him which was pretty bad.
The problem was not the introduction of the power lvls the problem was the author is not consistent to keep the representation as it is and the proof is looking at now when was the last time we saw power lvls? 286 was the last chapter we saw power lvls numbers now we are at 321 which means we are at 35 chapters without any power lvls the problem is exactly the same.
The thing is there are more things to determine someone's power aside from the power lvls and those are: Skills during a fight and how much damage they get.
The bigger the distance between the individuals in terms of of overall power the more damage the weaker gets with low tier skills.
Like let's pretend that meliodas power lvl never got introduced so he fights someone and he can beat the other with like basic lvl punches in his base form and he makes it look like he is also going easy on the opponent on top on that, the other guy seems to fight serious so we pretty much know he is not holding back and that meliodas is so powerful the other guy is like no challenge.
Now if all of a sudden you have the other guy suddenly start damaging meliodas out of his ass
you know that there is something really weird right?
The editor tries to make it look like the other guy was hidding power or some crap but when you see
the art and it looks like meliodas puts zero effort and the other shows effort so you realize there is something really weird.
You don't need power lvls to say to you that meliodas is stronger than the other dude but when the other dude suddenly start damaging the other guy you know that the representations is completely messed up because you are like: " but meliodas only poked him while been in his basic and the other guy got a damage from that attack so the opponent is a weakling and the conclusion is the editor tries his bullshits to hype out the fight"
For me the starting point was during the gallant fight because by making meliodas raising up to 10.800 power lvl downgraded the grey d hendy fight which meliodas used on his base form powers the whole time and the author made it like meliodas had such an difficult fight which ofc was not the case because if meliodas used the demon mark powers he would had destroyed grey d hendy without effort since he was more than twice as strong as grey d hendy even with a portion of his powers stolen by merlin.
That was the start of me doubting about the writing and ofc after gallant everything went from bad to worst.
After introducing us that meliodas power lvl after getting the stolen portion of his power made his at 30.000 he somehow manages to solo dolor and gloxinia and even went against the 9 of the commandments by himself and that revenge counter if it was not for the commandment of love of estarossa he would had killed them all at that point.
ofc we didn't doubt it back then didn't we? We were faithful because the text said they had their powers depleted by the magic seal and so they were weaker right?
Then what nakaba does? After like 2-3 months of timeskip and while we though the commandment had regained their full strength and we were expecting amazing fights with them been even stronger what good nakaba does? He brings us meliodas with even bigger powering boost and a curse of immortality but we all were like: " ok the commandments had 2-3 months so they replenished their powers so they will be much stronger" but then what happens?
Meliodas solos effortless derierre and monspiet, one punch after humiliating in a one-side
spanking fraudin, merlin effortless beats with one click of her fingers greyroad like he was nothing and makes escanor to beat like estarossa and zeldris....
I don't know like nakaba just tripped over himself and the writing fell from a cliff or something and died