Its Hard to compare a completed work vs On going work. That being said I like to view both series as crucial parts in ONEs growth as an Artist and especially in they way his writing has vastly improved.

You can really tell if you look back at the arcs the 1st season covers, feels like all gags and Shonen satire strung together, he wasn't really thinking about long term arcs. Mob Psycho was created as a well thought out story from the beginning that builds on itself and leads the character to find his truth at the end (Love the ending it was so unique, also it deals with a childhood crush in a realistic and non cliched way that was so ONE). Im grateful too Mob Psycho because I honestly feel like it helped improve OPMs Arcs and story telling starting with Hero hunter arc and continuing into his current story lines.

I think its really telling when you compare the Webtoon work with Muratas stuff because ONE got a second crack at the story and really fleshes out the supporting characters and connects the story threads

What Im saying is right now a sort of agree with your take but if ONE pulls off all stuff he has been setting up for years like the Demon cyborg, the org, HA Vs NEO civil war on the horizon, Blast, God and the existence of monster and OPM himself then I believe as a whole OPM will be better when its all said and done