I think most people would term that the class of 2019, not 2018 (this is the 2016 offseason right now).
A lot those players will either extend and not reach free agency or decline and not be a big deal three years from now. It's just so early to look at it.
Some of the names he lists even suck right now, lol. Gattis and Happ? Mauer? Carter Capps will probably be retired in three years. Nelson Cruz will be 38! He will be total garbage.
I will grant that the top end is massive and some of them seem to have a very strong chance of reaching FA. Harper, Donaldson, Cutch, Machado, Heyward, Kershaw, Fernandez, Sale could all be seen to have a better than average chance of still being elite and not extending with their current team, for one reason or another.