And yet, Jay Leno is still unfunny.
It's really difficult to accurately determine this situation, because it was so unique. Had NBC allowed Conan O'Brien to flourish, like they did Jay Leno, he might have found his groove and the ratings for his Tonight Show
might have stabilized. The fact is, Jay Leno was doing pretty badly in primetime, and they never should have given him a primetime show.
Which falls back to Leno. When NBC basically told him they were planning on replacing Leno with Conan back in 2004, he probably should have just went quietly into the night, like he was planning on doing, and then not spring the complete opposite on NBC just as Conan was about to takeover. It wasn't fair to NBC, who scrambled and tried to appease all parties, and it definitely wasn't fair to Conan.
It all doesn't really, matter, though, because now that Leno's been back on the air for a while his ratings will stabilize, and it was and never will be fair to compare his ratings to Conan, who's on basic cable, and doesn't nearly have the viewer base that Leno and/or Letterman can tap into. However, to be completely fair, Conan always had a niche sense of humor, which isn't exactly broadly accessible. He never really should have hosted The Tonight Show
anyway, since his brand of humor is more absurdest, and the type of humor that the show requires is more bland, mainstream humor, which is what Leno can provide.