I've actually seen an interview with Sting, where he brought up why he didn't go to the 'E' and it was that he basically didn't want to have to prove himself to Vince McMahon, when the fans all loved and respected him already. That's not exactly what he said, but it's the jist. He had an example of what he meant, which was when Booker T first did a segment with The Rock during the Invasion, Rock turned to Booker and said 'who the hell are you?' and that's when Sting 'knew' he'd never get respected and utilised properly in WWE.
But, tbh, it's hard to say. Were Booker, Goldberg, Mysterio, Benoit, Guerrero, Jericho buried in WWE? Fuck no. Every single one of those guys was crowned the champion, most of them after as little as 4 years with the company.
Then again, Simmons, Vader, Kronik, Gillberg, Raven, DDP, Saturn, Bagwell and a slew of others were hired and humiliated/ditched within months of joining. Others joined and then went into a backstage role and are still there now i.e Dreamer, Noble, Malenko, Anderson, Tazz (ok, he just left but still). And there's the odd ones like Finlay and Regal who've had half decent runs despite jumping back and forth between companys.
The problem with Sting is, that while he is an automatic draw like Goldberg for instance, he's got a pretty big thing going against him. Vince already has the Undertaker. Vince already has a big, sturdy veteran, with a succesful 'dark' gimmick who draws consistantly, so why would Vince want him?
Vince would probably make Sting start with the upper mid-card, and wait to see how well he could do before making him a ME guy. Vince would want to assess his ring work with the other WWE guys and just how prone to injury he is, and if he can still handle the WWE work schedule. Sting might want the same deal as Taker and HBK, with the lighter schedules, but Vince won't give it to him.
"You work your ass off to make me money for 2 decades like they both have and keep the fans attention, and THEN i'll consider it," would probably be Vince's answer to such a request.
I think Vince would probably give Sting the same sort of run that Benoit had. In Benoit's first year in the 'E', he fueded with loads of top guys including Jericho, Angle, Taker, HHH, Austin, and the Rock. So that's the company's 2 most popular up and comers and every ME guy they had at the time. He was even crowned the champion twice (ok both title matches were restarted and the title wins didn't count, but they still saw him as good enough to be in the ME scene very quickly.)
If Sting signed a contract with Vince and had Benoit or Jericho's attitude when they arrived i.e. "wow, i didn't know it was so awesome to work for these guys! Thank God i left WCW" instead of what was probably Booker T's initial attitude of 'ok you bought out the rest of my contract, but don't treat me like a nobody, i'm the 5 time blah blah blah', then i think Sting would probably have a great run in the 'E' that he himself would be proud of.......
.....Shame it's not likely to happen, especially after all of Foley's recent moaning about Vince.