Yes and no. If those guys never showed up, once the Rock and Trips and Mick and Stone Cold got over, the WWF was going to win anyway no matter what. WCW’s product was absolutely dead by the time Jericho showed up. The things that were set in motion that would get WCW kicked off Turner had already been moving along. Also, none of those guys won world titles before WCW kicked it, top guys should always get the credit for sinking ccompetitors.
The WWF was going to win the moment they went into 1999 with all of the ratings and live gates, true. The top talent signified that.
HOWEVER, this revisionism that Jericho and the Radicals jumping ship didn't matter much is ridiculous, as it soured the core WCW audience to the point where many switched off and just never returned. The WWF had an audience of casuals, lifelong fans, and hardcore smarks. WCW had
rasslin' fans, the kind that Corny used to talk about when he said "wrestling fans watch wrestling to see wrestlers wrestle," and when five of the company's best wrestlers left for the competition within a few months of each other? It signified that things weren't going to get better, and they tuned out.
The Radicals debuted on Raw on 1/31/00, and WCW only saw their Nitro ratings crack a 3.0 10x from then onward. Before that, Nitro ratings hovered in the mid 3's to the mid 4's for the majority of 1997-1999 (with dips into the high 2's starting in 1999). People may not have been tuning into Nitro en masse to see Benoit and Malenko, but enough of them left after they signed to the WWF and never returned to point to that moment as the last major turning point. Especially since Raw's numbers rose to the high 5's/mid 6's on average throughout 2000, where Jericho and Eddie and Benoit were being used often and in much higher profile programs than they were in WCW.
Jericho and the Radicals leaving didn't kill WCW, but it clearly signified that WCW was entering hospice care.