Top 5 according to whom? Not only am I calling bullshit on this, but back then there were no unified official rankings because of the UFC-Pride-other orgs separation and no way to accurately rank them. The competitors in the UFC were so weak that they would have artificially inflated rankings for being successful, compared to the Pride guys who had much stiffer competition. For example, I remember Ricco Rodriguez had a huge jump in rankings after beating Randy Couture, with some places listing him as the #1 HW, and others #2 behind Big Nog. Other than Randy, he defeated nobody else of note whatsoever, and neither did Randy; Pedro Rizzo was Randy's biggest win at HW and Rizzo was a fringe top 10-15 guy with one good win over Barnett. There was no way to accurately compare the two organizations, and thus the top 5 lists were varied and had no context.
You wanted facts? Ok, let's analyze your claims using historical rankings and archives. I can say with certainty that Fedor faced top 5 competition in Sobral, Schilt, Herring, Big Nog x2 (we won't count the NC), Coleman x2, Cro Cop, Sylvia, and Arlovski, for a total of 10. This is even when you consider the inflated rankings of the weak UFC HW division. Now when you extend that to top 10 to counter the inflated UFC rankings, you have to include guys like Kohsaka (1st fight), Randleman, Goodridge, Hunt, etc so we'll just say 14 top 10 wins for combined UFC, or top 5 Pride rankings to be fair without throwing in guys ranked top in other divisions like Lindland, or Brett Rogers even though he was technically a top 10 ranked guy. Not counting the UFC, these would be considered top 5, but again, those inflated UFC rankings. In the Heavyweight division which is known for having the highest chances of being KOed or upset.
Compare that to GSP. His top 5 wins include Penn 1, Hughes x2, Serra (who was only ranked because of one win over GSP himself, despite a middling career), Fitch, Alves, Koscheck x2, Shields, Condit, and Hendricks (highly disputed win). That's 11 top 5 wins. You pulled that 17 number out of your ass. Even if you extend that to top 10 and include Mayhem, Trigg, Sherk, Hardy, and Diaz, that's 16. Even if you ignore my previous point about inflated UFC rankings during the Pride era, that's still just 1 more top 5 win than Fedor, who fought in a division where it is much harder to string together wins. I can handle people thinking GSP is the GOAT even though I disagree, but to imply that Fedor isn't even close is the dumbest thing I can think of in MMA.