That's probably true. I'm not a big fan of Joe Rogan's standup but he has his moments, and he's clearly a funny guy when he's with his friends. Ari is not even funny when he's in a room with people, but to your point, he does seem very self-absorbed. I know comedy is subjective though, and that's just my opinion.
I disagree. His tweet was about as unoriginal and hackish as any typical internet troll making a misguided attempt at edgy humor. It was basically, "Good! I'm glad he's dead! Liberal Hollywood! The Lakers suck!" That's not unrelatable because of it's so high-brow that people just don't understand, or so novel that people just weren't ready for it. It's hack humor, if it can even be considered humor.
If there are any solid Ari Shiffir bits I'd be willing to hear them out. But I've seen a bit of his material over the years and it's never funny but always grating.