I'm not saying that Pronger's season was a fluke or he didn't earn it he certainly was a force on the ice. The best player league wide I could understand some debate about so I won't argue that. His season was realistically almost a carbon copy of MacInnis' from the previous year. The only big difference is +/- which considering he averaged over 30 mins a game and the team as a whole gave up over 40 goals less well simple math takes care of that. Lets not discount Turek's performance that year.
Now that's a rudementary view for sure. But there are more factors than individual play that go into +/- and to take that stat from his year with caution. While certainly Norris quality season I'm not sure if I could say it was the best out of that decade.