Sure Roy and Brodeur were on better teams than Hasek. And Hasek played great in the playoffs.
But how many times did Hasek carry his team farther than it should have gone? Once in 1999.
How many times did Roy carry his team farther than it should have gone?
If you look at the actual matchups both goalies faced in the playoffs, this is closer than you might think.
Record in playoff series for Hasek and Roy, broken down by whether their team was superior to the opponent, fairly even, or inferior.
When their team was 6 or more regular season points better:
Roy: 22-5
Hasek: 7-0
When their team was within 5 regular season points of the other team:
Roy: 8-2
Hasek: 3-3
When their team was 6 or more regular season points worse:
Roy: 2-6
Hasek: 3-5
Most of Roy's playoff edge came because his team was usually better than the other team. Also, while this doesn't fit exactly into the playoff category, most of Hasek's teams wouldn't have made the playoffs with an average goaltender.
Hasek also carried his team in the playoffs more often than in 1999. In 1998, Buffalo was 17th out of 26 teams in goals for, and allowed the most shots against in the regular season. They beat Philadelphia (6th in regular season points) and Montreal (12th in regular season points) in the playoffs, before losing to Washington (8th in regular season points). Hasek had an 0.938 SV% that playoffs. Without Hasek, Buffalo probably doesn't make the playoffs that season, so the conference finals would be a clear overachievement.
Also, in 2001, Buffalo beat a Philadelphia team that had more regular season points, goals for, and fewer shots against.
Even in 2001-02, while the Wings were better than everyone else, Hasek beat some very good teams. The Blues were probably as good as the Wings outside of the goalies, and of course Colorado and Patrick Roy were always a tough matchup. (Yes, you could say the same for Roy's playoff runs also. I'm just saying that it's not like the Wings would have won with any goalie in net that year.)