Actually I think he's just undervalued.
Much of the debate these days focuses solely on the current greats (Fed, Rafa, Nole). When historians step in to argue against their status, they usually bring up players from a mystical yesteryear like Laver, Rosewall, Gonzales and Tilden.
Sampras seems to have become seen merely as some sort of 'stepping stone' for current greats - i.e. to surpass his 14 slams, ~285 wks as No 1, etc. Few actually care to analyse why he was such a great champion.
He really didn't care about minor tournaments, so those obsessed with percentages always have his win-loss record to put him down. But the man himself played for far loftier goals, and could care not a jot.
He's 3rd all time for me behind only the true GOAT contenders, Federer and Laver...