We put too high a value on size in todays game. I would say prime height of solid players are in the range of 5'9 1/2" to 6' 4". There are certainly players doing well outside both of those ranges but they are the exception instead of the rule. My point on Kuz would be that if he were a little smaller, with the exact same skills, he likely wouldn't have even had a shot to play in the game. (or if he were on the smaller side of average). The players outside those parameters that make it in the NHL are an exception and Kuz so far isn't looking like one of them.
I think you've come to the same conclusion that Detroit's scouting staff had as a revelation 5 years ago after drafting terribly for almost a decade- average size and great skillset is much better than good size and poor skills.
Yeah, Kuznetsov is lucky enough to be born big so he can collect an NHL paycheck for awhile.