Everyone in the UFC (or any serious MMA org) trains a mix of striking and grappling these days. At those early UFC’s when it was single-style vs. single-style, the BJJ guy (Royce Gracie) did win. (Royce of course had been training BJJ since childhood, so he’s not a great example of your point about overlooking experience.) Of course it helps that the strikers probably didn’t know what the heck a gi choke was, whereas Royce had surely seen a punch before.
Anyway, since that time there have been plenty of successful MMA fighters who were primarily strikers (Chuck Liddell, Mirko “Crocop” Filipovic, Maurice Smith, etc.), but they had to learn enough takedown defense to keep the fight standing where they could put their striking to good use. In general, the best fighter is the one who knows how to defend against his opponent’s techniques, which is why everyone in MMA trains a little of everything.
It’s true that Tae Kwon Do is far from the striking art of choice in modern MMA (most prefer Muay Thai, or a full-contact karate style like Kyokushin, as well as western boxing), but I think that has more to do with the fact that TKD practitioners don’t usually spend nearly as much time training full contact sparring, and have more restrictive rules compared to Muay Thai (no leg kicks, no knees or elbows, no clinch fighting, and for some organizations no punches to the head), which makes their training less relevant to MMA. (That said, there are quite a few MMA fighters who trained TKD in their youth before taking up a more full-contact oriented style.)
My point isn’t “TKD is as good for MMA as BJJ”, but rather “The smart fighter uses a hybrid of different styles, including striking and grappling arts.” Saying “Martial Art X is the best” makes no sense anymore, because the best guy in that style will still lose when he goes up against a modern fighter who trains a little of everything.