Keep in mind the era - league average SV% was around .910 at the time. Those numbers were far less impressive then than they would be today.
Went from a top performer to average performer to out of the league within 5 years. That's with a bunch of missed time in between.
He burst onto the scene, but also played on a Very Good Anaheim team where his teammate also posted .922 save percentage in Hiller's rookie year.
Giguere was starting to fade and Hiller it seems should have been played more, but aside from 08-09 Hiller's sv% was comparable to a backup.
Ray Emery technically had .926 (in only 10 games) the season he was an all star (Granted, Hiller's Save % would have been impacted this season by the vertigo).
I'm also curious about the difference between top and bottom end goalies. 08-09 Hiller crushed it, but in 09-10 even with a very good .007 above league average he was still only 10th in the league in save percentage among starters. Very good, but also closer to median (15th) than the top spot.
I think there's also something to be said about the team in front of him, given the fact that his early Anaheim career he joined a team that had a defensive corps that would have still included players like Niedermeyer and Pronger. In only one season did Hiller get a Vezina vote: the shortened season he split with Victor Fasth. This is a subjective measurement... but I would dispute the assertion of a top goalie for someone that the rest of the hockey landscape does not feel is the same.
Here is the age graph for goalies. Hiller's drop off should also not ignore age as goalies tend to peak in the late 20s (right when Hiller did).