The discussion of whether or not Alex Galchenyuk was rushed has been split into a lot of different strands and is thus harder for others to follow. I will try to streamline it,
@Sorinth.
I think that Galchenyuk was rushed. He was one of the least developed players to ever play in the modern NHL, he was not ready for the NHL, and this may have undermined his development.
Galchenyuk entered the NHL with 109 CHL games played and 7 WJC games played. He only played 8 games in his draft year, as he suffered a significant knee injury. Moreover, during that time, he would have had to train less. While his peers were developing their strength and their skating, in addition to his hockey sense, he was doing physiotherapy and applying ice packs to his knees, while no doubt losing strength.
If we look at some comparable, Brenden Gallagher, who was a rookie teammate on the Habs, played 280 games in the CHL including two deep memorial cup runs. Nick Suzuki got 308 games in the CHL, including two substantial memorial cup runs, including one where he was the leader. Sidney Crosby, a vastly greater talent than Galchenyuk, got 143 games of CHL experience, and a greater number of WJC games. Jonathan Toews, who was the comparable for Galchenyuk in his draft year, played 42 WCHA games in his draft year, 34 WCHA games in the year after that, and got to play in 2 rather than 1 WJC.
Alex Galchenyuk simply didn't get as much time in overall play before making the NHL, nor did he get to simmer and dominate for an extended period, nor did he get to lead his team against greater competition, either at the WJCs or in a memorial cup run. He just didn't get to do any of that. He was rushed to the NHL, perhaps out of a perverse old school belief that he should be allowed to "make the team out of camp", or perhaps to help the Habs make the playoffs.
Galchenyuk came into the NHL lacking strength, lacking skating ability, and lacking defensive awareness. He was not trusted to play on special teams. He did exceedingly well at 5on5 -- a skill that he would lose later on in his career -- but he did so in limited and massaged minutes, playing with Gallagher and Eller on the 3rd line, and having guys like Markov, Subban, and Diaz feeding him the puck. He never got to progress after that.
To say that Galchenyuk was rushed is not hindsight, as many of us including myself were calling it at the time. It is also not valid to say that other players have been incorrectly labelled as rushed, as Galchenyuk is one of the the least developed rookies in the history of the modern NHL. I've written this in multiple posts, and you have not been able to bring up several comparisons. I'm guessing it's because there aren't many.
You did bring up Joe Thornton as a counterexample, but that fails. Thornton had 120 games of CHL experience, he played 50 games in the WOHL, and he was a 1st overall talent who went on to a hall of fame career.