It's been a while since I read the Clouds. IIRC, it was a lot of scatological and Mae West style humor (i.e. "Is that a sword under your tunic, or are you happy to see me?").

Aristophanes has literary value, but he was just exposing holes in Plato's logic for comedic and theatrical value; he was not himself a serious philosopher.

... Serious Philosopher.

Isn't that the whole problem expressed in two words?

Euclid was arguably "more serious" as a philosopher than a mathematician -- his principal contribution was to build a logical framework around others' results.

I want to start punning now -- who was more serious, Edward Teller or Richard Feynmann? -- but it's not useful. I'll simply note a certain dissonance in calling Diogenes serious, as you seem to.

Just remember how important the fool is in Shakespeare...

Leo Strauss would say otherwise. He has a whole book about Aristophane's take on Socrates, highlighting the crucial tension between the philosopher and the rest of society - the reason Socrates was killed. According to Allan Bloom, the whole enlightenment project can be explained as an attempt to solve this problem by displacing religion with philosophy, through science.