I think the thing people are ignoring a little bit here is that Ken Jennings has the quality many of the other guest hosts didn't - you believed he knew the answers.
Trebek probably knew half-to-2/3s of them, and that's better than most, but you always believed he knew them. And that is unmistakably a key factor to the host of this job. The reactions to right / wrong answers have to be quick, have to be surprised when a really bad answer happens, or sympathetic when there were 2 good answers and they picked the wrong one.
It's why Katie Couric came off so weird when she was like "look at all these SMARTIES". Like, this is Jeopardy! it's a pinnacle of the US Trivia Circuit, and it should be treated as such. This isn't a bar room quiz bowl, these are elite competitors who have trained years or months for this chance and moment.
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The other thing is someone brought up Drew vs Bob on Price. I don't think anyone could quickly "settle in" to Price is Right, considering that there are basically zero other audience participation shows out there to learn the ropes with.
Much like Bob Barker, no one will ever be Alex Trebek. But you don't need to say "genre" the same way as Trebek, or set up contestants the way Bob Barker did to be successful. Dre, in his sense of humor, his clear appreciation for the game and ability to root for the contestants, and the way the show has been pretty radically reworked around him over the last 15 years (and radically cut down too due to more ads!), have reached a point where everyone realizes that he isn't Bob, but he's a great host of The Price is Right.