The term that was used was "the best". Full stop.
Most productive? Ok. Using extrapolated stats to produce extrapolated results, you get that he is a more productive goal scorer at ES than Ovechkin or Kane. Or Malkin. Or Crosby. You can truly tell me that you believe that he is a more productive ES goal scorer than those 4? If you do, does that not mean that you want him out there in ES situations more than those guys? If you say no, then I need to question why you would want the most productive even strength goal scorer on the ice.
Since Nash became a Ranger in 2012-2013, here are the 5v5 numbers for these players: (Corsica).
Ovechkin: 368 games, 5339 minutes, 97 goals
Kane: 341 games, 5308 minutes, 96 goals
Crosby: 348 games, 5204 minutes, 92 goals
Nash: 315 games, 4076 minutes, 86 goals
Malkin: 279 games, 3295 minutes, 70 goals
Take a really close look at these numbers, and make sure that this is the hill you want to die on for hating against per 60 metrics.
I can truly tell you that Rick Nash, since 2012-2013, is the most productive 5v5 goal scorer of this group of players.
Do I want him out there in 5v5 situations more than these guys? I don't know. That's not what these metrics tell me. I need more information.