What you say is a kind of interesting. It shows that you didn't watch the match, because Sampras was playing very well. I don't think that he was playing his peak tennis by any means, but a very good level nonetheless.
However, you are not following: win or lose that match Federer played S&V in it and to a great effect, and that was the main contention: that he mastered that style. The fact that he won just helps to bring the point home, which would have been more difficult with the trolls which even now refuse to recognise the facts.
Your way of arguing is extremely volatile: you are trying to move goalposts, create straw men and your work with facts is lousy.
When we started talking you claimed that Federer hasn't won anything big on fast grass, to which I responded with several achievements of his own in such conditions.
You then proceeded to falsify basically every point I made:
To the point about winning the Junior Wimbledon in Singles and Doubles you said that it doesn't count, because it wasn't even Wimbledon, which is patently false. Then you tried to create a straw man by saying that Junior Wimbledon is not as important/difficult to win as the men's tournament, when I never claimed that.
To the point of Federer winning against Sampras, you first claimed that Sampras had a "bad day at the office", and after I made the remark that you didn't watch the match, if you claim such a thing, you shifted your claim to "Sampras had a bad year" (as though a player has to play badly everywhere, if he has a bad year).
To the point of his first Wimbledon win being achieved with significant amount of S&Ving, you try to sweep under the carpet that that style was a significant part of what won him that tournament, even though the grass was already a lot less conductive of using that playing style.
In your efforts to disprove my points you forget to disprove the fact that all of these were achieved while playing S&V to a great effect.
You say that those are not big achievements, but they are as big as they get, considering the place where the career of the player was. I mean, if Federer plays in the Junior ranks, he cannot win more than the Wimbledon for Juniors (both for Singles and Doubles no less), can he?
Beating the King of Wimbledon with his own style that he never had a chance to develop fully and would later abandon for a more adequate to the conditions is as big a testament to his mastery and learning ability as any.
Using a style that was already dying out while winning his first Wimbledon: another big sign of ability in adverse conditions.
The truth is that Federer was extremely promising fast surface player, and the only thing stopping him from developing even earlier was his game that needed time to mature.
I cannot answer definitely the question of whether Sampras or Federer would have been better on fast grass. Sampras was a beast on the serve, and athletically very gifted, but Federer had better return and could match and exceed Samp's efficiency on the serve and definitely had a bigger serve plus FH combo. Federer really spend very little time developing his fast-grass game.
He entered the men's tour in 1999, and by Wimbledon 2002 the fast grass of old was gone.