I think that GMs are slightly overvaluing size. While important, it's clearly not compulsory to be big in today's NHL.
I recently analyzed every forward taken in the drafts between 2005 and 2010 and found some pretty revealing information regarding height and NHL success:
Of all the forwards drafted during this time who were 6' or taller, 45.6% played at least one game. 23.4% played 100 games or more. The total points per game of all these players is .47.
Of all the forwards drafted during this time who were 5'11" or smaller, 48.8% played at least one game. 24.2% played 100 games or more. The total PPG of all these players is .501.
There's a disgustingly pervasive myth that smaller forwards have higher "bust factor" than bigger players. What I found is that this common narrative is absolutely not grounded in reality.
I did not analyze defensemen, but I would hypothesize that size does play more of a prohibitive role. But as far as forwards are concerned, drafting small, skilled players like Gaudreau, Kucherov, etc. is no more risky than drafting bigger players. Teams have been handcuffing themselves for years by ignoring talented small players in favor of bigger guys who they believe are more likely to carve out NHL careers. It's just not true. Teams like TB with no size bias are laughing their way to highly successful picks that others seem to ignore.
Just another example of the NHL's frustratingly conservative and traditional approach to analysis rather than analyzing empirical data to determine where successful picks lie.
EDIT: This also brings me to another frustrating misconception. Often times a team will draft a highly talented, small forward, and you will hear the phrase "high risk, high reward". This is an asinine statement. For ALL players drafted, there exists risk of the player never playing in the NHL. But for some reason, the risk is only acknowledged for smaller players. Take a pick like Tyler Biggs. Most people said, "Oh, well even if he doesn't reach his potential, he can still be a bottom six guy because he has size". Wrong. That's BS, and now he's no longer a legit NHL prospect. Tell me how that pick was any less risky than he Panthers selecting Rocco Grimaldi a few picks later. It wasn't. There's a dinosaur mentality in the NHL, and the people running the show are petrified of breaking from conservative tradition, instead relying on empty rhetoric that gets perpetuated year after year.