Is he? I always thought Robertson was about 6'1/6'2. He does not play like he's 6'3 210. And NHL teams almost always inflate player heights by about an inch, so I'd suspect he's closer to 6'2, if he's listed at 6'3. I've found some sources since his NHL career started that stated he's 6'2.
As for Pastujov, he's listed at 6'0 by every source, but looking at those NTDP measurements, a lot of those kids look taller than the listed height. NTDP does not inflate player heights, so if Pastujov was 6'0 at the start of the season, there's a chance he may be taller now. He still hasn't turned 18, so he could still be growing.
Regardless, I think the point I was making goes beyond just comparing the players, even if Robertson ends up being 3 inches taller. Size is not an issue for Pastujov. It may end up a slight strength, but he has the type of offensive ability that Robertson had. The players who weak skating usually impacts disproportionately are the small players. Players can overcome being small or being weak skaters. They often cannot overcome both.