There's an argument to make that government-imposed price ceilings cause market inefficiencies, but not as much when it comes to salary caps. There will always be a supply of hockey players. But it is true that trades are far more difficult to propose, and that's where the inefficiency comes into play.
With regards to the quality of the league, it is true that rich teams were not guaranteed success in the past. But without the cap, you did have a lot of clubs winning the Cup back to back years, having dynasties for several years. That was partly because they could keep all their young guns and offer them hefty salaries. Nowadays these clubs don't have that luxury. But then again, one could say the Red Wings have a dynasty.
Positives and negatives. It's also a good thing for investors in the NHL as well, especially when I see wages in the Premiership being inflated into oblivion. But when I look at a division like the Southeast with all these expansion teams who are consistently rubbish, I can't say outright that the cap has increased the competitiveness of the league.