You do realize that Roshi was actually the strongest human on earth at the point, right? Regarding the red army he only stated that he wasn't sure about having the STAMINA to handle them. Much different from AP, speed, durability and allat.
Also, Roshi blowing the moon to undo the form of someone who could probably solo the verse at that point doesn't really sound like a gag to me.
"Oh, look at Goku, he is using the same transformation that killed his grandpa and that's probably going to kill everyone else!! Lmao, that sooo funnnn πππ.*