When did the main event change from being at the end of the card? LMAO, the last match on the card is always presented as the most important, and generally what sells the shows. With the exception of WM24 anyway. I'd check back into reality before claiming my argument's weak if I were you.
And since now it's just about Triple H, I certainly have my doubts, and his matches before he got injured weren't exactly classics. He and Sheamus did some nice things but it was hardly main event material. Whether he's capable of doing it and proving me wrong remains to be seen. In fact, his absence has yielded 0 negative change to the Raw ratings whatsoever. I don't know how him not being a true WM main eventer is asinine, since he continually underdelivers when pushed as the no. 1 guy. His use is in comedy DX mode or feuding with younger guys. There's no evidence (to my knowledge anyway) to show he'd make a significant difference in buys, and i'm not holding my breath on a match to get people talking the next day.
Wrestlemania 24 is your example. Rock vs Hogan was also billed as a main event for Wrestlemania 18. They also advertised this year that with Edge winning the Royal Rumble he would be in the "main event at Wrestlemania," and there were three matches after that. But this point is moot and we're arguing over semantics here, when the rest of your post is the real problem.
You state that Triple H "doesn't have it anymore," presumably talking about big time matches, not in the undercard. In fact, you yourself state that his role should be feuding with younger guys, so I suppose we have to be talking about big time matches. My point is that Triple H had one shitty main event, and so you jump to the conclusion that he doesn't have it anymore? What, that he can't go in the ring? That he can't convey a good story? It's just such a huge jump that it doesn't take into account reality. Triple H has been out of the title scene for like thirteen months, if you count his one-off title match at Survivor Series. Before that, he hadn't had an extended title feud since Wrestlemania 25 in early 2009. Compound that with the fact that he has been completely off screen for like eight or nine months. There can't possibly be any Triple H fatigue at this point.
The complaint through the mid-2000's that Triple H was overexposed were completely legitimate, and it was a good reason to argue against him being in another Wrestlemania main event. But to conclude from one shitty match that he magically can't do it anymore reeks of Irrational Triple H Hate Complex. Again, I'm not at all the biggest fan of the guy, but I'm not going to conclude that Wrestlemania 25 marked some sort of turning point in his career that meant that he couldn't perform anymore. Especially when you look at the fact that he was as solid as he could be in the Chamber the month prior, and actually legitimately good in his program with Jeff Hardy just before to that. So, if he could go then, he magically couldn't a few months later, and a shitty match with Orton proved that? And even when he returned, he got a lot of praise for his work with Legacy that summer. I disliked all of it because fuck DX, but it worked.
Or is it that he proved that he can't go at Wrestlemania, specifically? As if working a 'Mania match is a completely different category from working a wrestling match. Oh, he can put on entertaining matches in May, August, November, and maaaaybe December, but March? Shit no. He can't work a match in March, because one match proves it so.
Or is it that he can't draw? Because, judging by 2010 buyrates, neither can anybody else in the WWE then. Good storytelling sells PPVs, which is probably why this year's TLC was the only one since Wrestlemania to supersede the prior buyrate. A big angle for Triple H to come back and make his way to Wrestlemania to win the world title is compelling storytelling. It's more than just "hey you beat me up backstage let's have a PPV match." If he comes back, wins the title at 'Mania, and then stays in the title scene all year, then maybe he wouldn't be as big of a draw the next year. But, looking at things in context, a Triple H comeback and Wrestlemania main event is good storytelling for over the next few months. So, I don't see how his current position could prove that he "doesn't have it anymore."
I had to cover all my bases, because you weren't explicitly clear in what you mean that he "doesn't have it anymore." Still though, I can't see any logical context in which you could legitimately say that Triple H vs Orton at Wrestlemania 25 in itself proved that he "doesn't have what it takes anymore."