The guy who made that chart first wrote about the idea on The Hockey News last summer, so it's not behind a paywall:
http://www.thehockeynews.com/news/ar...to-win-the-cup
It's based on "Game Score". I have no idea how valid this is as a stat, and I can't find anywhere that actually shows the current Game Score rankings for this season.
Based on the rankings from last summer (using projected numbers for this season), Gio and Hamilton were the Flames' two Tier 1 players; Gaudreau and Tkachuk were Tier 3; Backlund was Tier 4; and Frolik was Tier 5.