There's a major flaw in your argument. It is that you are comparing "the best" <180lbs guys with "the best" >180lbs guys. But that's not really the choice. The "best" big guys will have jobs for sure. But there are a bunch of big guys that aren't skilled in the league. Would you rather Jimmy Hayes or Sebastian Aho? Ryan Ellis or Duncan Siemens?
Easy choice sure, because we know how they turned out. But there are a growing number of scouts, stats guys and prospect watchers who are pimping the smaller skill guy over the big guys who haven't scored a lot but "boy if they ever find that skill they'll be great" guys.
In a perfect world your team would be the biggest, fastest, strongest, most skilled, hardest working, toughest guys in the world. But there are only so many of those guys. It comes down to do you want to take a chance on a guy who might have immense skill but less than ideal size or a guy with ideal size but less skill.
In today's game, it's becoming clearer that the former are the better gamble.