Also, it's incredibly difficult to take a goalie's stats to do a comparison as the rest of the team has responsibilities in keeping the puck out of the net as well.
If the goaltender replacement are equal or above to your usual replacement and play enough game (some year that would be hard for Brodeur) it can give some idea.
For example from 1994 to 1999 the Buffalo Sabres when it was not Hasek playing in net had a .897 save percentage, they were a mix of Fuhr, Shields, Trefilov, Roloson, Biron, etc... because Roloson played only 18 games and Fuhr was getting old nothing that specially good or bad supporting cast. That around exactly the nhl average save percentage of that era.
Hasek during that time frame was .930, if a team giving their number one the best opponent in 2 games in 2 nights scenario and what not it can underrate a bit how much better they were, if they play their stars goaltender at home more and are better at home overrate them, etc... but it is probably much easier to have some idea of how many goals were saved by Hasek playing instead of a reasonable easy to find replacement than how many more goals are added by any forward playing over a reasonable easy to find replacement, that the part of the equation that specially hard.
A lot of team way to keep puck out of the net is done via shoot count not influencing the save percentage, which can happen some Claude Julien-Hitchcocks teams seem to have been able but it is rare, at least not more common that players scoring being influenced by the rest of the team responsibilities in putting pucks in the net, minutes-deployment-linemate-power play, etc....
