You make it sound like the whole game is silly. For the most part, the story itself (And when it comes down to it, Jonny as well) tends to stay pretty serious. Jonny just got a couple bad lines, and people hound him for it.
Thgouch Charlotte is still comic relief, but then again, So was Maria Renard for the most part. Boobies story, anyone?
In any case, just because the entire story isn't dark and brooding doesn't make it a Saturday morning cartoon. I sure as hell wouldn't want kids watching stuff like Black Lagoon. Besides, the Japanese already have a Castlevania spinoff parody. It's called Kid Dracula.