I noticed how nobody in this thread acknowledged your post about the comparison to Lowry. Lowry was who immediately came to mind as a comparison for Gauthier.
Lowry was touted as a big, defensive C who needed to work on his quickness.
The main differences are: 1) Lowry is very physical and aggressive. Leads the Jets in hits this season; 2) Lowry was actually a very good scorer in junior in his draft+2 season (was injured for most of his draft+1).
Lowry's skating has improved markedly since being drafted. He could still work a bit on quickness, but he moves very well for a 6'5" player.
In his Draft +2 year Lowry scored 45 goals averaged 1.22 points a game and was named WHL player of the year. This really is is a lot better than the 16 goals and 32 points in 37 games Gauthier put up at the same age. Lowry was simply a MUCH better player at the same age.
In addition to being injured his draft +1 year Lowry had Mono his draft year and was one of the 1 in 20 kids who was still growing at 18. His skating issues were more around stride and quickness, but part of that was undoubtedly the due to him growing 10 inches after he started playing in the WHL, which can mess with skating. Speed was never really an issue for him, he's always been relatively fast once he got moving.
While there were some similarities up to their draft +1 year with Lowry you could still pick out reasons why he was underachieving offensively, which isn't really the case with Gauthier IMO.