For a better presentation of the contemporary view of philosophers like Plato, you should read Aristophane's Clouds. It's also alot deeper in meaning than a mere facile mockery of poorly understood ideas.
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.
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.
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.
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.