I'm not a McDavid fan, but he's technically a very good skater, everyone in the NHL skates like him, but he's one of the faster skaters. As his back leg comes up and over during a cross-over, the back leg doesn't get blocked by the front leg's shin guard because he's so deep.
Here's a super-deep position, in long-track speed skating. The front leg crosses over but doesn't come close to touching the back leg and knee.