The stars that left WWE for WCW was only part of the equation. What really pulled WCW ahead of WWE was that they started doing something different in prime time against them. They weren't trying to be a cheap imitation of WWE, they went and did their own thing and had confidence in doing so.
If the WCW/NWA had a prime time show on TBS back in the mid 80s when they had the Horsemen, Dusty, the Road Warriors, etc they would have done amazing. Their shows were so much better than WWFs. But instead JCP was sold and the leaders of WCW just copied WWE as much as possible. Ugh. Even in the late 80's they could have done great.
Even from day one when Hogan debuted in WCW, I always said he should be a bad guy there. His first match was Flair (the best of NWA/WCW) against Hogan (the best of WWF) in a WCW ring and Hogan won in his first match there, like WTF!!! When WCW did shows in WCW territory, the fans literally booed Hogan everytime, but yet they pushed Hogan trying to mimic WWE.
So yeah I give Bischoff credit for having the guts to be like, yeah give me a weekly prime time show and did things differently. Then WCW became stale and once WWE changed their formula and retook the lead, WCW fell back into just copying WWE again.