The only problem I have with them taking the main event spot is I don't get Machida vs. Hendo 5 rounds. I am having potentially 5 rounds of greatness reduced to 3 because a no-name is going to get arm barred by an average at best fighter in the first round.
As for them main eventing outside of that, it's a championship fight and champions fight in the main event, that's just how that works and I'm not upset about it beyond what I mentioned.
As for it not selling well, we will see what the final numbers.
I understand your logic behind Machida/Hendo getting 25 minutes but I think people's expectations for this fight are pretty high, I'm under the impression many see this as a possible Shogun/Henderson type fight when there's no chance it turns out like that at all.
If this goes the distance I have a feeling it won't be competitive, and more likely one sided in Machida's favor. He's just too crafty to get caught by the H-Bomb, he got dropped by an overhand right from Shogun but he fought out of character, he was too aggressive and that's not the way his style works, if he remains patient and is comfortable with picking Dan apart then I think he'll take it comfortably.