Why? Is it a drawback for every player playing juniors right now? The ONLY reason he's in the NHL right now is his draft pick and size. So he is able to sometimes look fine because of his size. But more often than not, he's lost. It's going too fast. He needs to learn how to walk. Strangely, they've realized it with Mesar.....but somehow don't have the ego to do the same with Juraj.....
Most observers see the huge, enormous difference in quality of play on ice between Mesar and Slafkovsky.
The priniciple in development is to play at the best level you can play at without getting favours over currently better players, and without being starved of playing time. And no, 12+ minutes is not being 'starved'.
Most 16 year olds in the CHL start on the 3rd or 4th line in October, even though they could be killing it in Midget AAA.
Most 15 year olds in Midget AAA could be killing it in Bantam AAA or Midget AA.
The bulk of prospects played at the highest level at which they could look decent, and this for their whole lives. Most would then, according to their long-term potential, improve at each level, the best of them heading toward standing out.
In an age category that is 2-4 years long, it normally takes a half season, maybe a whole one in the CHL, to start standing out. In the pros, it often takes longer as guys don't graduate out due to being too good, they only drop off due to age or injury.
Holding guys back to allegedly increase confidence is just not a research-supported developmental path. Perhaps it is useful to a small minority of athletes, but it is hardly a standard.