An interesting stat is that PK joined the NHL full time at the age of 21, when he accumulated 38 points in 77 games, good for 5th on the team. To make the jump as a D at that age as a 2nd round pick is pretty amazing.
I also consider him a "winner". He's been proven to score clutch goals, (tying the game in the final minute of game 7 vs Boston, sniping one passed Anderson in game 4 of the playoffs last season when it was do or die) and he won gold at the WJC. He also has that extra gear that elite players, that allows him to out compete about 95% of his opponents if need be.
As for Galchenyuk, joining the NHL full time at the age of 18, after missing just about his whole draft season with a busted knee, is just phenomenal. He has all the tools he needs to become that coveted #1 center man that we've been looking for for decades.
His skills are very well documented, but he draws similarities to PK in another facet of his game. In my eyes, he's also a "winner" and silent leader (see Toews). He leads by example on the ice, and this only at the age of 19. He tries to compete hard every shift.
He's also come up clutch. Last season, he tried several times throughout the regular season to snipe one top shelf, only to miss the net. Then, in that do or die game 4 vs Ottawa, he snipes one farside at a near impossible angle, when it mattered the most. Aside from that, he helped his relatively underdog team win the WJC, a tournament that by all accounts should have been won by a powerhouse team Canada, and he scored 2 goals in a shootout to win Bronze at the world championships.
All in all, both these players are franchise players at their respective positions. They have all the skill in the world, but what separates them from their peers is their character and will to win; Subban saying the other Norris winners have a Cup and he doesn't, and Galchenyuk nearly shedding tears after losing in playoffs as a rookie.
PS: I picked Galchenyuk, but we are truly blessed to have them both, and I really do believe that they will one day hoist a cup wearing Habs jerseys, one with an A and one with a C!