There's no mystery as to why dubas has picked up first Campbell and now mrazek. Unsurprisingly, it's based on stats.
Over the last 5yrs, 50 goalies have faced at least 2500 shot attempts. Here's the top-30 goalies in terms of dfsv% - basically a stat which tracks the difference between a goalies save percentage and his expected save percentage based on the quality of shots he faces. Here's the top-30 of those 50 goalies the last 3yrs:
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So Dubas is betting on a stat that's probably at least similar to this one here. He bet on it when he grabbed Campbell and it worked out very well so far, so we can be pretty hopeful it will also work out with Mrazek.
And Mrazek's place on this list can be explained by team stats as well.
Over the last 3yrs, the Canes have been the #1 team in hockey in terms of fewest shots allowed - letting up 28.17 shots against per 60min. But, they are much less impressive when it comes to shot quality - over these 3yrs they rank only 17th in xga/60 at 2.81. That combination of elite in shot prevention but mediocre in chance prevention is obviously the worst thing for a goalie's save percentage.