John Oliver hosts a late night talk show and he is primarily a comedian. He is not a journalist so your commentary on journalism seems misplaced on this point.
As he is primarily known as a comedian, there is no way to confuse him as a journalist doing "news reporting". This calibrates the critical thinking dial in my brain.
> Given that he throws a joke from time to time, does it mean that it's less reporting and more comedy?
Have you watched the show? The joke to content ratio is very high.