if you could go back in time, would you warn WCW and Booker T of their fates?
Booker T yes. It wouldn't have done much and would have been horrible money wise, but I can't help but think how much he could have built for himself with the last year and a half of ECW roster where he could have been "it", then a much fresher start in WWE.
That said, he really didn't have a bad fate. Sure G.I. Bro was awful, far too many burials early on in WWE, but where the guy is now with Hall of Fame, his own wrestling school? The guy is doing okay with plenty of happy moments.
WCW? It depends on just how far back. If before Eric Bischoff, sure. I could warn them about the horrible spending, the terrible waste, the environment that made talented and dedicated wrestlers just not care any more, and so much more. Perhaps they wouldn't have gotten as big, but a solid number two without so many problems TNA has.
With Bischoff? No, not at all. No matter what it was always going to spend and waste too much, trying to burn and salt the land until WWE was dead. So giving them some warnings? It would have just lasted longer with WWE perhaps going out of business, then WCW collapsing and decreasing to a point where even modern British television wrestling would look down on it with pity.
Now if I really could go back in time and fix things, it would be the 70s for British wrestling, getting those promoters to put more into the industry and build it into something bigger rather than coasting along just happy it's so popular until it fades away.
Perhaps giving warnings to Pro Wrestling USA. Just imagine if that had actually managed to not have so much infighting, internal politics, feuding between promoters, and a clear grasp of what it meant to actually go for television and PPV/closed circuit like WWE did.