But it sure makes it easier when he comes to North America and is an IHL goaltender...
I'm not really understanding the disparaging of the Hasek's 1990-91 season in the IHL. In context, his numbers look just about as dominating as we might expect Hasek's numbers to look in a sub-NHL league. The key thing to note is that Hasek's playing partner in 1990-91 was Jimmy Waite, the IHL's First Team All-Star Goalie from the previous season (1989-90). Hasek came in and completely outplayed Waite:
Hasek: 20-11-1, 2.52
Waite: 26-18-4, 3.47
Here's the league GAA leaderboard for goalies with 30+ games played:
1. Hasek 33 GP, 2.52
2. Hebert 36 GP, 2.87
3. Guenette 43 GP, 3.26
4. McKichan 30 GP, 3.32
5. Waite 49 GP, 3.47
6. Sharples 37 GP, 3.55
7. Dyck 38 GP, 3.66
8. Beauregard 32 GP, 3.71
9. Weeks 37 GP, 3.78
10. Myllys 38 GP, 3.79
11. Gosselin 46 GP, 3.86
12. Clifford 56 GP, 3.97
13. Goverde 40 GP, 4.10
14. Brower 37 GP, 4.11
15. Chevrier 32 GP, 4.40
16. Flaherty 56 GP, 4.49
Hasek is lapping the field with the exception of Hebert. However, Hebert played on a Peoria team that led the league in scoring and goals against and finished first in the standings by a wide margin. Hebert's backups during the regular season combined for a 3.29 GAA (and an impressive win/loss record of 34-9-4), meaning that Hasek's GAA edge over backups was over twice as large as Hebert's. In the playoffs Indianapolis was eliminated in the first round without Hasek (who was in Chicago). Peoria won the IHL championship with a goalie platoon of Hebert and Pat Jablonski, with Jablonski actually playing in more games during the run, making it even more obvious which goalie was actually doing the most to drive his team's results.
The IHL scoring average that year was 3.92 goals per game. That means that Hasek's GAA was 64% of league average, 0.35 ahead of the top goalie on the stacked best team in the league and 0.74 ahead of everyone else, including nearly a full goal per game better than his teammate who had been voted the best goalie in the league the previous season. I don't see how that can be interpreted as anything other than a goalie who was way too good for the league.
Hasek was the best goalie in the IHL and ended the season in the NHL as the backup in Chicago during the playoffs, stopping 121 of 132 shots in the regular season and playoffs combined at the NHL level (.917). Given all that together with the fact that Ed Belfour won the 1991 Vezina Trophy, I think that's about all that could be reasonably expected for Hasek's first professional season in North America.