1 - Ziggler is just as over as Jeff Hardy was. Hardy left WWE at the peak of his popularity so we don't know if he would have gotten more popular, but I can say with no doubt whatsoever that Dolph Ziggler winning the World Heavyweight Championship on the RAW after WrestleMania 29 got a MUCH bigger reaction than any of Hardy's three World Championship wins in WWE. And other than the last few months where he's been stuck on the irrelevant Kickoff Show, Ziggler continues to be one of WWE's most over stars, despite how hard Vince tried to bury him. Even as recently as WrestleMania 32, Ziggler got a bigger reaction than anybody except for The Undertaker and Triple H (who had the unfair advantage of going AGAINST Roman Reigns, so he was treated as the second coming).
No, he really isn't, and to suggest so is to undermine Hardy's ridiculous popularity in 08/09.
To be fair to Dolph, his two biggest chances to rocket to the moon - his MITB cash-in and post-Survivor Series 2014 - were derailed by injury and bad booking, respectively. Ziggler was white-hot 2-3 years ago, but you can't expect that to last after being consistently booked as HBK's jobbing doppleganger. Just because you're cheering loud enough in your living room to drown out his typically "Meh" reactions doesn't mean Zigglermania is running wild.
And no, Ziggler did not get a bigger reaction at Mania than New Day, HBK/Austin/Foley, AJ Styles, The Rock, or Sasha Banks.
2 - So you'd rather see a complete nobody like Baron Corbin get a title shot at the 2nd biggest show of the year than a proven draw like Dolph Ziggler? Or Bray Wyatt, who loses even more than Ziggler does and has never been able to be a top star despite dozens of opportunities handed to him? Nobody deserves this spot more than Ziggler.
The complete nobody that came out on the winning end in his feud with Ziggler? Yeah, I would have.
Bray Wyatt has consistently bested Ambrose in every program they've had with each other, whether it was Wyatts vs Shield, Bray vs Ambrose, or Wyatts vs Ambrose & Reigns. If anyone has Ambrose's number besides Seth Rollins, it's Bray Wyatt. Given their history, he would be the favorite and a far more intriguing opponent than Ziggler, who I recall coming up short against Ambrose in every match they've had against each other in the last year or so.
3 - You mean the match at SummerSlam 2013 which stole the show right out from under Punk/Lesnar and Cena/Bryan, and was one of the best matches of the year? I think Ambrose and Ziggler would be fine with that.
I and many, many others would say Punk/Lesnar and Bryan/Cena, two bonafide MOTY candidates, far outshone Del Rio/Christian (which was still a good match). But if you prefer it, more power to you.