The real problem that hasn't been addressed here is the culture shock that Leno fans will go through starting Monday. Let's face it, Fallon is very different from Leno. For some, "different" is hard to take. He's a little edgier. He's a lot younger. His band is extremely edgy for the time, especially in the Midwest. No question he'll attract the big name guests. He's been able to do that for five years. No question he'll create an entertaining show. Leno had been going through the motions on this second trip. But none of that addresses the culture shock.
What some forget is that when Leno took over the Tonight Show 22 years ago, he'd been doing fill-in guest hosting for years. That had also been the intent of Joan Rivers before she walked out and took her own show. These days, there are no guest hosts. There is no period where we get used to someone new. Same with Letterman, Kimmel, and everyone else. They run repeats rather than build the next generation. Some of that is contractual. Leno's show was produced by his own company. Same with Letterman. The network doesn't want the previous host to pick their own successor. The network wants to do that. So we get these abrupt changes that often don't sit well with audiences, particularly older audiences.
There was an article recently about how traumatic radio format changes are for listeners. I expect we'll see the same thing here. The difference is that they don't have Leno as a lead-in to late news. That was a far bigger problem the last time than the weakness of Conan. So they're flying without a net here. I predict it will take some time for Fallon to achieve the kind of dominance Leno had. I saw Letterman's interview with Brian Williams a few weeks ago, and it's obvious that this new competition at 11:30, and the fact that it's originating in NY has Dave pretty fired up. So he's got new shows next week. Fallon has the Olympics lead in, but Letterman will start a half-hour earlier. Wonder if Dave will mention it.