Hasn't the premise been set that the Saitama really can't be challenged? No attack yet has actually done anything to him. He got blasted to the moon with no ill effects. His speed changes with whoever he is fighting at the time, and his strength appears to be limitless. I guess if they take him to space he dies since he can't breathe.
You're focusing too much on the trope. It's a gag series, where a planet level character was essentially dropped into an entire world of street-level characters, and a few high tiers that couldn't even take on the likes of Boros(planetary, at best).
It's widely accepted that Boros was the strongest character other than Saitama, thus far- and even he was only capable of destroying the surface of Earth, with his strongest attack- in his strongest form.
It's very similar to how Superman would be, if there were no other super-beings in his series.
We go by feats here, and based on feats- Saitama would stop at #2.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
We’ve seen him get “super serious”. At that point, he was capable of overpowering a planet razing attack from Boros. This makes Saitama roughly a planet level character, which is honestly even a stretch, based on that feat. There is, afterall, a HUGE difference between planet razing and planet BUSTING.
Even if we were to assume that attack was only 1% of his power(which wouldn’t make sense, considering he himself called it “Super Serious”), that would barely make him a planet buster at full strength.
Of course any of this can change, but saying “wait and see”, is sheer childishness, and in outright denial of the fact that based on what we’ve seen- Saitama can’t compete with anything above an average Kryptonian.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
Never let anyone else define you. Don't be a jerk just to be a jerk, but if you are expressing your true inner feelings and beliefs, or at least trying to express that inner child, and everyone gets pissed off about it, never NEVER apologize for it. Let them think what they want, let them define you in their narrow little minds while they suppress every last piece of them just to keep a friend that never liked them for themselves in the first place.