Oniichan's subject matter might be risky if it was aiming at a general audience, but seeing as it's a late-night show being sold specifically to an otaku audience pre-programmed into buying such fanservice fetish series, it's not really doing anything new or creative really at all. As you said, it's "basic." Chowder might not seem particularly different from a lot of the shows now, but think back to what else was airing on CN at the time: My Gym Partner's a Monkey, Class of 3000, Out of Jimmy's Head. Chowder in comparison was different in that it was the first storyboard-driven show the network had made in years and allowed for weirder humor and mixed media experimentation. I mean, it's not totally unique, Spongebob and other shows had done similar things in the past, but networks seem nervous about more offbeat comedies a lot of the time for some reason, so it was a mild risk. At the very least, it wasn't a sure-fire success like Oniichan.