Editor's note: Ed Bark, former longtime TV critic of The Dallas Morning News, blogs about TV at the website unclebarky.com.
(CNN) -- There's presumably no going back this time. Jay Leno is leaving the "Tonight Show" on Thursday after nearly 22 years as host. Jimmy Fallon, with less than five years on NBC's follow-up "Late Night" shift, takes over on February 17. His successor, "Saturday Night Live" mainstay Seth Meyers, is set to step in a week later.
It's still not clear exactly why NBC is dumping Leno, the king of late night in all key audience measurements, including advertiser-prized 18- to 49-year-olds. He's well ahead of Fallon, David Letterman, Jimmy Kimmel, Conan O'Brien, Jon Stewart and Stephen Colbert. NBC programming executives' only explanation, in the network's initial April 2013 announcement, was that "Jimmy Fallon is a unique talent and this is his time."
But Leno does leave a legacy, and it's not just repeatedly taking it on his ample chin from both NBC and countless detractors. Nor is it the fact that his departure will likely set off a wave of new tensions in the late-night landscape (more on that later).
I think Leno's stature slowly will improve with age as the undisputed "people's champ" in times when TV critics for the most part dismissed him as a lightweight. Letterman, O'Brien and Kimmel have been deemed the "smart," inventive late-night hosts, but Leno has arguably been the hardest-working man in late night -- even if as a plodder, not a craftsman. And ratings don't lie.
Leno's principal strength, as was Johnny Carson's, has been his extended monologues. He can reliably reel off jokes in assembly line fashion, making "Tonight Show" an easy, effortless tune-in. Follow-up segments such as "Headlines" and "Jaywalking" also have kept audiences from going elsewhere or going to bed.
But the second half of Leno's "Tonight Show" has been the show's soft midsection. His patter with guests invariably feels preordained. Jack Paar, who had a comparatively short run in the "Tonight Show" chair in the years before Carson, was the show's pre-eminent conversationalist. As guest Betty White noted this week, nothing was rehearsed or prescrubbed with Paar. You winged it, and you'd better have something to say.
Carson relied far more heavily on "blue card" crib notes that have become talk show staples during interview segments. But his big, boisterous laugh could break out at any moment -- infectious for viewers and the sound of music for any guest who could get a rise out of Johnny. Leno mostly titters under his breath, more schoolgirl giggler than full-throated bonhomie. Still, he has kept the ratings singing for NBC, and in a much more crowded late night universe than Carson ever experienced.
Leno, of course, can't touch Carson, the program's acknowledged "gold standard." And Carson made it no secret that he wanted Letterman, not Leno, to succeed him. All these years later, Letterman in reality is the only late night host who even belongs in the same conversation with Carson.
For his part, the 66-year-old Letterman is good to go through at least 2015 via a recently signed deal with CBS. But I wouldn't particularly want to be him once Fallon takes over "Tonight Show." For the first time in his long tenure at CBS he'll have to compete directly against a New York-based host who also happens to be a generation younger.
That could be a serious problem when it comes to attracting a more contemporary collection of guests during the New York legs of their publicity tours. (Justin Timberlake, for one, already is basically a member of Fallon's repertory company.) But it could work quite well for Kimmel, who now will have the West Coast all to himself opposite his NBC and CBS rivals.
Letterman also will be the last of the late night "social media" Luddites after Leno walks the plank. In contrast, Fallon is a skilled Twitter practitioner with 11.4 million followers. Fallon is also a deft impressionist and accomplished sketch player; neither are Letterman strengths.
What Fallon doesn't have so far is Leno's monologue gene. He'll have to lengthen his joke-telling segment, which could ripen in time. For now it's easily the weakest part of his game, giving both Letterman and Kimmel the openings they might need -- both literally and figuratively.
Fallon's big plus is a big kid likability that makes him easy to root for. His humor can be barbed, but he clearly aims to please. In contrast to Letterman and Kimmel, he always wants to be his guests' -- and his audience's -- very best friend. But there's no discernible edge. Even Leno throws an occasional jab.
In truth, NBC's latest late night moves could and probably should have waited a few more years. Leno has done nothing but win and win again with no signs of weakness. As a further indignity he's being sacked as a 63-year-old even as NBC is developing a new sitcom for the 76-year-old Bill Cosby. Out with the old, in with the older.
One more intriguing thing: Meyers, at age 40, is a year older than Fallon. NBC's later slot historically has gone to a host who's a generation younger, with the idea of grooming him for the "Tonight Show" desk.
But if Fallon succeeds -- and that's certainly what his network wants -- might NBC in effect be showcasing and setting up Meyers for a jump to a rival network someday? After all, he presumably wants to move up at some point, too. But where would he go? Pardon NBC for just not wanting to think about that right now.
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The opinions expressed in this commentary are solely those of Ed Bark.