I haven't watched any kind of wrestling in over a decade and don't usually post here but you're really missing the point.
What Sting did during the early NWO saga is arguably the most fascinating narratives in wrestling period and nobody else was in a position to or had the quiet charisma necessary to pull it off.
It only worked because in the years preceding the NWO's emergence Sting was WCW's favourite son, If I remember right he was actually referred to as "The Franchise". He was at the height of his early popularity before Hogan turned heel. The transformation to "dark Sting" worked because it represented what the fans felt about the Outsiders and Hogan at the time and Sting decided to embody that.
He wasn't a heel or a face he was basically a deus ex machina. People forget the significance of him coming down to the ring through the fans and dropping down from the rafters. He made himself a representation of their will.
That's why he could walk into the ring and solo the entire NWO, that's why Hogan and Bischoff had to act shook whenever he was around; because they're all at the mercy of the fans and they wanted to see their scorned favourite son set things right.
It doesn't matter that it didn't happen within actual matches because between the fake stings, false masks, dropping down from the rafters, the silence, the baseball bats, the saves, the loyalty tests etc... shyt was exciting and isn't that ultimately the point?
Realistically Sting could have made the Jump to the E (There were many offers) and found a way to work the gimmick into something equally successful there but he saw how former stars like Booker T were getting clowned and had to start from scratch and didn't trust that the same wouldn't happen to him.
who in the blue hell are you? - YouTube
The fact that he's now slumming it in TNA and Taker was able to further cement his legend has everything to do with the end of WCW and dominance of WWE. There is no conceivable way in which Taker could have jumped to WCW and performed the same role or built up the same kind of rivalry with Hogan.