This. Even without the major WCW stars Invasion had a huge buyrate for a non Mania. If he had stood up to his wrestlers and hired some of the big guys he could have made an insane amount of money. Even if he didnt hire the big guys the Invasion buyrate proves the audience could have been convinced to accept the WCW guys as a big deal if they were treated as such.
This is really revisionist. Who could he bring in?
Kevin Nash? One of the main reasons WCW died (behind the scenes). Had a guaranteed contract with TimeWarner until the end of 2001 that was higher than anyone in the WWF locker room, and had no intention of letting go of it, and if he signed for anyone, he lost it. When he did sign, he was too injured to wrestle at first. While he was rehabbing, he injured his bicep. Finally, five months after his on-screen return, he tore his quad walking to the centre of the ring after taking a tag, finally executing his first wrestling move in a ring fourteen months after his on screen return. Not an option.
Scott Hall? Fired in under 90 days after the plane ride from hell, was the last in a series of final straws on that European tour. Only made it to Wrestlemania because he was paired with Austin and there was no alternative opponent (Benoit was pencilled in, but not recovered from injury in time). Austin being paired with him at Wrestlemania caused Austin to walk out the first time. At the time, only worth anything at the box office with Nash. Not an option.
Scott Steiner? Not medically cleared. Had one atrocious match for the ill-fated WWA in Australia. And by the time he signed, just not up to the in-ring quality of the WWF anymore. Not an option.
Bill Goldberg? No passion for the business. Like Nash, he had a huge guaranteed contract with TimeWarner until 2003. TimeWarner eventually paid it up, and McMahon spent months negotiating. And Goldberg didn't want to go on the road, just to TV and PPV only (a huge factor in the fall of WCW was the stars not doing house shows, and also caused a major dip in business in WWE in 2003). Not an option.
Sting? The year he spent in the rafters killed his interest in wrestling and he wanted to be a movie star. Another guaranteed contract (March 2002) that he didn't want to waive. Had zero interest in signing for McMahon, as he didn't want to work a schedule, and he didn't like the sexual content. Did two short tours, but only wrestled 19 times in the five years after WCW folded. Not an option.
Ric Flair? Was already 52. Like Nash, Goldberg and Sting, he had a guaranteed contract, but settled his early to sign. He would have been a better mouthpiece, but people just didn't want to see him as a heel (something else that screwed WCW, and WWE in 2003), and could have more than carried his weight in a tag match, but not as a regular singles competitor.
Hulk Hogan? Had initially refused to sign because of his lawsuit against WCW/Russo over the Bash at the Beach work/shoot. A one-PPV nostalgia pop wonder. After his Wrestlemania match with the Rock, Vince puts the title on him at Backlash, and the buyrate isn't great, Judgment Day where he loses the title is worse. Use him at Invasion, and you waste that one buyrate. Save him for Summerslam or the final showdown at Survivor Series. But a several month long program? No. They both knew it though. Hence had him putting over Angle and Lesnar, before Hogan threw his toys out of the pram, because McMahpn wanted him to put Lesnar over again. Came back a few months later for another nostalgia pop, and the short lived Mr America storyline which he quit before the payoff for "creative" reasons (ie, he had to job too often, and someone else got the spotlight).
Eric Bischoff? McMahon tried to sign him, but Bischoff turned him down. Tried to start up a company called MatRats, which never got off the ground.
Don't get me wrong, the Invasion was screwed up, but not because of who wasn't signed. It was screwed up because of how they treated who they did sign. DDP and especially Booker T should have been positioned as bigger threats than they were. Jericho could have been added to the Alliance side as a third threat (Benoit was injured), and RVD could have been elevated (although he wasn't making friends by potatoing opponents left right and centre). But DDP was already 45, and the top WWE guys were in the prime of their careers. Undertaker was the oldest main eventer at the age of 38, and was older than all the WCW main eventers. Booker was the only WCW main eventer under 40, and he's slightly older than Taker.
Even with all that, the main reason the Invasion failed was that McMahon's ego got in the way (much like Jim Crockett's did when JCP bought out the UWF), and he had to present his guys as better than the failed opposition in every way.