Are Asian stereotypes the only thing people have to say about this show? No one seems to notice the fact that Christy Hui, the creator of the series is, in fact, Chinese and was raised in China.
Not to mention that while Omi is yellow, something everyone points out, most of the other Asian characters are not.
And underdeveloped characters in a Y7-rated cartoon? That's not exactly new. Need a cowboy character? Well, you better make him the cowboy-iest character you possibly can; small children usually don't understand complex characters, so I doubt they one day thought: "Hey, how can we offend Texans?" and thus Clay. Especially considering that he's actually pretty smart, not to mention level-headed and polite, there's very little about him that I'd find insulting.
And while the four main characters may not be deep, they all have their own personal issues, such as Omi and Raimundo's MASSIVE egos, which often have negative consequences.
If you look past the apparent simplicity of the characters and the shiny action scenes, you may actually find it's not as shallow as it seems. Life lessons about teamwork and friendship and that.
And this coming from someone who's really only in it for the villains.