At the time that Sting first debuted a lot of fans were interested in seeing some dream matches finally happen. The number one match on every ones mind is that Sting could finally step into the ring with The Undertaker. However, things didn't work out that way due to well the WWE being the WWE in many fans eyes. Now do I think that Sting & Undertaker could've carried a good match together at Mania, honestly I do think so. But it would have to be kept in mind that both men were into their 50's and may not have been able to have the type of match they could've had in their prime.
Once Sting arrived in the WWE he was in his mid 50's and yes he was still Sting, but not in his prime. I think it was a lost opportunity that Sting didn't arrive in the WWE sooner; had Sting left TNA before 2014 and arrived in the WWE sooner he may have been closer to his prime and with more of an opportunity to see Undertaker & Sting. Is it unfortunate Sting did end up in the company I don't think so, but overall I don't think his run went as well as it could've been had he arrived sooner.