VVD was already the best CB in the league at Southampton, and Alisson was one of the handful of world class goalkeepers at Roma, both were obvious world class players by the time we even signed them.
Like I said I think people are viewing what I define as a 'star' player as different. In my mind a 'star' player almost means a household name. Someone most casual football fans would identify as top of the tree in terms of football players. That's a bit different to identifying someone as a world class talent. Completely correct to say that van Dijk and Alisson were World class or on the brink of it. Same for Salah and Mane. We gave them that extra push (through coaching and playing with better players) and the platform that playing for a top club provides.
Buying a star player in the past would mean buying Figo, Ronaldo, Zidane, Nedved, Cannavaro, Buffon, Casillas, Raul type level players.
Nowadays it would probably be Haaland, Mbappe, De Bruyne, van Dijk, Salah, Lewandowski, Neymar, etc..
As an example I wouldn't label Jude Bellingham or Dusan Vlahovic type players as 'star' players despite both having world class level ability/potential.
The only star player I think we've signed in the last 20 years is probably Thaigo.