Cavemen was just too intelligent

You never gave any examples of why AD is not subtle. Just so you remember, you said you would provide examples, which you didn't.
You want examples that it was subtle-you mentioned in your post that something subtle requires background info for a joke. So, I'll tell you four that I can remember off the top of my head that appeared in AD:
1.)The narrator mentioning to the audience that the bad comment about Opie made by a character was a wrong choice. The narrator is Ron Howard, who played Opie in The Andy Griffith Show.
2.)Barry Zuckercorn jumping over a shark in an episode. Barry Zuckercorn is played by Henry Winkler, who played The Fonz in Happy Days, where he (in)famously jumped over a shark, where the term originated.
3.)Barry Zuckercorn raising his fists with his thumbs outstretched, looking at a mirror and saying "Aaay". The Fonz did that on Happy Days.
4.)Justine Bateman plays a prostitute who Michael believes to be his sister, but is ultimately wrong about that assertion. In real life, Justine Bateman is the sister of the actor who plays Michael.

I know those are not that funny, but that's only because you haven't seen them in context. Additionally, your definition of subtle is very narrow. In general it means, "difficult to understand or perceive" and "having or marked by keen insight and ability to penetrate deeply and thoroughly". Most of AD's jokes fit this definition, but even by your narrow standards, I was able to name four that I could immediately remember.
Now, I haven't watched Cavemen, but anyone who says AD is not funny is just plain wrong.

I blue myself.