I disagree that he has any particular skill that is notable. He was also a lousy comedian, most remembered for his crusade against joke stealing than anything else (I dare you to ask anyone their favorite Joe Rogan joke).
He had first mover advantage. Then he started to realize the right wing hits were drawing his viewers, and went further in further in that direction.
I think the chain of causation would be a step too far removed. He isn't indicted for instigating the riots, but for the conspiracy around rigging the electoral count. The riots are implicated as one tool to pressure Pence. Sicknick's death would also be another step removed in that it is not as clear that it was a direct result of the riots (or at least it could be argued). Babbitt maybe but I don't know how DC handles death of confederates which is another wrinkle in the felony murder rule.
Source: got a B in criminal law