What proves he isn't when he didn't even face any meaningful exertion from stopping an attack that was at least multi-continental? lol. Boros said at the end that Saitama wasn't even serious during the fight. Saitama literally said himself that he has the ability to destroy Earth but no, 'That was just hyperbole because no way he's that strong'.
Good that most readers acknowledge his strength.
Good that most readers acknowledge his strength.
Anime Saitama is Planetlevel but not the canon Version