That is a silly argument indeed. Were Chelsea 2012 or 2021, or Liverpool 2005, or many other examples full of world class players?
Responding your other question:
Rivaldo, Shevchenko, Zidane, Figo, Rui Costa, Batistuta, Veron, Nedved, Raul. All of them were better(some of them WAY better) than their United counterparts.
My point isn't that those players weren't equally fantastic but rather that there's a lot of gatekeeping when it comes to what counts as 'world-class'. A good number of United's treble-winning team would have got into any team in the world at that point and they proved it with their qualities both domestically and in Europe that season. I think anything else is adhering to the notion that being world-class is reserved for players who are basically in line for a Balon d'Or, which I reject as it's my fundamental belief those two categories should remain distinct. One is like the TOP TOP bracket and the other is just the TOP bracket. I think you could have 20/30/40 players at any point who can fit into the world class demographic.
And yeah I'd put a few players from Chelsea/Liverpool in there:
Liverpool 2005: Xabi Alonso and Gerrard
Chelsea 2012: Essien, Lampard, Cech, Ashley Cole
Chelsea: 2021: Rudiger, Kante
I should also point out that you listed a lot of forwards and you'll notice I didn't include any from United. I don't think any of Yorke, Cole, Sheringham, or Ole were world-class, to be honest.