Chris Jericho, The Big Show, and Sheamus are main event talents. Just because WWE has an intense hatred of veteran talents the last few years, doesn't change that. Two weeks of good booking and any of those guys are instantly at the top of the card again.
Jericho can be a main eventer for a PPV or 2, sure. Of the three you've mentioned, he's the only one with any sort of heat. Sheamus has been a dead duck since WM28, failing to come even close to his previous popularity levels. Look at his title run last year. Nobody cared.
Big Show is just done. I don't even mean that in an insulting way, I just think that he's been overexposed to the point that the only way for him to drum any real interest in the product is to book him in attraction type matches. Big Show vs. Shaq at Wrestlemania? Lots of press, lots of buzz. Big Show vs. Rollins at Summerslam? Nobody cares. Just look at the last few times he's had big PPV matches. The match with Reigns was awesome but other than that, it's all snoozers.
Rusev and Cesaro could also conceivably be moved into the main event scene very easily.
I agree but I gotta say, I'm shocked to see you say this. Here's a direct quote from you:
Rusev is still awful in the ring and will be jobbing on Superstars within a year
Link for source. That was almost 2 years ago. Do you not see the irony here? He ran through all of the veterans that you love so dearly (and who most people don't care about any more) and you raged all over the boards about it. Now, you think that he can be moved to the main event scene easily. You starting to understand how booking works now? All of those wins gave him credibility.
RAW is in much better shape than SmackDown, who have Dean Ambrose, John Cena, Randy Orton (who's injured so much he's barely worth more than Lesnar), and then IF they pushed them, they could potentially remake main event Superstars out of The Miz, Dolph Ziggler, Alberto Del Rio, and Kane.
They also have Wyatt and Styles who, despite your personal feelings, are more popular than any of those guys. Styles is widely considered the best wrestler in the world right now. Wyatt has suffered multiple setbacks but still remains popular.
The Miz is perfect where he's at. He doesn't have enough heat to justify moving him up the card and they've booked him extremely well since WM.
We've gone back and forth on Ziggler forever but since I'm trying to keep this civil for once, I'll just say he stinks and leave it at that.
Del Rio, when motivated, is excellent. I think that if they turned him face and built him up to be the guy to take the title off of Miz, he could improve his stock immensely and move back up the card. I don't see it happening though.
Kane: see Big Show.
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As for the topic at hand, I was very happy with the show tonight and Balor getting the clean win over Reigns was definitely the icing on the cake. I definitely think that whatever Smackdown comes up with as their main event at Summerslam, likely Ambrose/Cena or Ambrose/Styles, will definitely end up being the more marquee matchup. Hell, Orton/Lesnar may even end up closing the show. But this match is probably going to steal the show.