Do you need a great goalie to build a defensive system? Some would claim that whenever there is a combination of team and goalie that have a run of success that the team was able to build their defensive strength around the goalie. Does an elite defensive system require a great goalie, or is this reasoning false?
To answer this question, let's imagine a team that has a brick wall as a goalie. Yes, a 4' x 6' brick wall in net. The other team cannot score no matter how many shots it takes. What kind of strategy should that team use? Should it play a tight defensive style and try to minimize scoring chances against at the expense of offence? Or should it take every offensive risk possible, since it only needs one goal to win the game? Obviously the latter is the correct strategy, since there is no risk to giving up scoring chances and shots, and a very strong benefit for taking risks to score goals (any goal = guaranteed win). And conversely, what about a team playing with no goalie in the net? What kind of strategy should they use? In real life, teams often use an aggressive strategy with no goalie in because they are trying to tie the game, but what if there was no goalie and the score was tied? Such a team would obviously play very tight defence, because every shot on net becomes a goal. Therefore they would be very defensively focused to try to prevent shots at all costs, using a tight defensive shell and pressuring the puck carrier to block their shots or force a turnover that may allow a chance on the counterattack.
This is why claiming that a goalie is responsible for a defensive system is completely wrong. Grant Fuhr supporters may or may not be right about some things, but one thing they are definitely right about is that a great goalie is valuable for an offensive team because it allows them to take additional risks to try to score goals. If your goalie is better than the goalie on the other team, it makes sense to play a more open game with more shots on each net. If each team gets 10 shots of equal difficulty, a journeyman goalie could easily beat a Hall of Famer with a little luck. If both goalies face 60 shots, on the other hand, it is much more likely that the better goalie is going to win the game for his team.
With Dominik Hasek in net, the defencemen on the 1999 Buffalo Sabres were aggressive on their pinches, knowing that even if they gave up an odd-man rush it was likely that Hasek would make the save. In contrast, last year's Ottawa Senators played a tight defensive system and blocked as many shots as possible to try to protect their inexperienced goaltender Ray Emery. Both were the correct strategic moves, and helped them reach the Stanley Cup Final, since the trade-offs in terms of allowing/preventing scoring chances against were to their team's benefit.
Playing a defensive system does not indicate that there is a strong goalie in the net. On the contrary, a strong defensive system is most needed and most beneficial when there is a weak goalie in the net. With a great goalie, a team should take more risks to try to generate offence, since the star netminder reduces the risk of giving up extra goals from the additional scoring chances allowed.
This is also why it is so important to adjust goalie statistics for team factors. Great defensive systems can hide weak goaltenders, just as poor defensive systems can make excellent goalies look average. With the advantages of a great defensive team, a truly elite goalie should dominate, finishing at or near the top of the league in save percentage and GAA, in addition to getting their wins and shutouts. If a goalie posts an average save percentage on a great defensive team, that is a strong indicator that he is being covered by his teammates. The same thing, in reverse, can apply to goalies with a high save rate on bad teams, as their teammates may be taking a lot of risks to score and leaving their goalies open to high-quality chances against and making their performance more impressive.