The 2012 NHL entry draft is, with hindsight, one of the all-time worst drafts. However, it was not expected to be. I remember the discussions at the time. Nail Yakupov was seen as a future 50-goal scorer and Habs fans were sad that they did not get the 1st overall pick. Ryan Murray was seen as a franchise D, though maybe his injuries derailed him. And Galchenyuk was seen as a future franchise C, people compared him to Toews, Kopitar, and Hossa.
None of us can be 100% certain of the truth of drafting versus development for each individual player. But for fun, I'm going to compare what happened with Galchenyuk versus guys that the Habs might have drafted instead.
Alex Galchenyuk, 3rd overall, the guy the Habs drafted
109 CHL games and 7 WJC games played prior to entering the NHL.
12:19 TOI/game in his rookie season, 14:24 TOI/game in his second season.
Morgan Rielly, 5th overall, the guy Bergevin claims he wanted
154 CHL games, 14 AHL games, and 6 WJC games played prior to entering the NHL,
17:38 TOI/game in his first full season, 20:20 in his second full season
Filip Forsberg, 11th overall, the most successful player of that draft year, that many fans wanted
91 games in Sweden prior to entering the NHL, also got 47 AHL games and 19 WJC games.
17:20 TOI/game in his first full season (2014-2015), 19:03 TOI/game in his second season.
Teuvo Terevainen, 18th overall, the guy that Timmins was rumored as considering at the time
137 games played in Finland prior to entering the NHL, also got 13 WJC games, and 44 AHL games
12:47 in 2014-2015, where he was a rookie and played half a season. In his first full-season, he played 15:21 per game.
Relative to the more successful players of his draft -- which is already a biased comparison -- Galchenyuk was hampered by inferior development. The other players typically had ~50 additional pre-NHL games relative to him, were given more ice time to develop in their first year, and more ice time in their second year. It may be that those players would have turned out better regardless -- but it is also the case that they got superior development. They were not rushed to the NHL so that they could spend more time sitting on the bench.