This cartoon is based on a Japanese manga called "Kinnikuman" that originated about 20 or more years ago. That manga was about the adventures of an alien wrestler on Earth, and it spawned more mangas, several cartoon shows and a toy line that is still highly collectible.
In other words, it's got a respectable past behind it, even if it wasn't originally seen in the US.
I don't think it would spoil anything if I told you that yes, here, the hero is a coward and a slacker. But if you observed the show, you could see the character evolving and taking more responsibility. I think that it's kinda cool, where, even though Kid Muscle is obviously terrified, he still ends up doing the right thing and helping his friends.
If you want angst in yer anime, go watch Evangilon Genesis. Otherwise..
Pull my finger!