I agree with this. The bottom line is that at the end of the day, short of cheating, a win is a win, whatever the reason.
However, when comparing player's greatness, you can't say that Djokovic's wins over Federer in 2014 and 2015 make him a greater player. Sure, greater and better those years, absolutely. However, it doesn't really say anything about Djokovic vs. Federer in terms of greatness, except for the accumulation of Majors. So Djokovic gained on Federer, but at the end of the day its still Djokovic with 12 Majors, Nadal and Sampras with 14, and Federer with 17...and then the stats on weeks #1, YE#1, ATP Finals, Masters etc.