Can something be both a "marquee brand" and in third place?
The Q3 nightly average:
Late Show with Stephen Colbert: 2.8 million viewers.
Jimmy Kimmel Live!: 1.8 million viewers.
The Tonight Show Starring Jimmy Fallon: 1.2 million viewers.
This to me is like calling something "The Cadillac of..." in the 1990s.
NBC doesn't sell a "brand". It sells viewers to advertisers.
I think (and I've said this before) Fallon stays as long as Lorne Michaels is in charge of NBC late night programming. Once Lorne's gone, all bets are off, and not just for Jimmy, but for the show itself.
As for Carson---by the end (not counting the parade of stars during farewell week or month or whatever), I think his was primarily a 55-plus audience. So 88-plus now.
I'm about to turn 70. I like Johnny. I watched Johnny---sometimes. Overall, though, that was my parents' show, and I was thrilled when Letterman came along to turn the genre on its head.