yeah... the argument is he's a joke character with no limit
based on showing he performed planetary feats with no effort whatsoever, cracked the moon with a jump, a cloud splitting punch that countered planet surface wiping blast
he probably so far used less than 5 percent of his full power
but krillin after dbs power level is at least final form frieza at the end of namek saga
base frieza can take out planet vegeta (much larger than earth due to it's gravity) with one attack, and that was at his base form
so yeah... Krillin can def compete with OPM, unless we add one hella no limit fallacy on OPM
Even by the end of the Namek saga, Krillin's PL was 75k... Which would already make him a casual planet-buster.
And DBS-era Krillin is VASTLY more powerful than he was on Namek, and multiple sources confirm that he is still the most powerful earthling(ie. Krillin > Roshi, Tien, Yamcha, etc.)
So yeah, short of applying a huge no-limits fallacy to OPM, there is no way to logically argue that he would be even remotely close to Krillin's level.
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
Saitama is basically a comfortable planet buster living in a world where those who are seen as the strongest beings (Boros and Garou) range from multi-continent level to probably moon level as far as raw power goes.
And final form Garou and Boros are like literal gods to the rest of the cast.
Serious Saitama >>> Boros, Garou >>> S class heroes (on average) >>> everything else
Of course if you put a being of the caliber of Saitama against city busters he would seem like a God. And indeed he is.
However, as Galan said, at the end of the Namek saga Kuririn was already more than 4 times more powerful than a legit planet buster (Saiyan saga Vegeta).
And then he kept on getting stronger to the point that probably between the Cell saga and Boo saga he should have approached at least the million mark.
Not to talk about DBS ToP Kuririn.
Just beacuse he is a joke in DB it doesn't mean that he is not strong in his own right.
In OPM, Kuririn would be an untouchable midget God.
Krillin is ridicuously more powerful than anyone in OPM... because Saitama is a joke character, they can make him more powerful than Krillin, but for now Krillin wins.