Gauthier isn't progressing as hoped. However, I do dislike the comments that classify him as a third liner and then say they are easy to get. All third liners are not made the same. If you want a sub-par or decent third liner you can get them easily. The reason Gauthier went so high is not solely because he's regarded as a safe pick, it's because it was believed he could be a rare kind of third liner, the type that you generally very rarely get on FA. And if you find one, you'll have plenty of competition and likely have to overpay.
Gauthier can still progress to become a player that can put up a decent amount of minutes while giving size, physicality, possession and elite defense. So perhaps he will not be as good as hoped offensively, but he's not so bad that if you give him some skill on the wings he won't be able to support them.
Either way, that's still a valuable piece and a decent catch for a late first. The homerun potential seems to have disappeared, but in my opinion he is still looking like someone we'll be glad we have in the future.