While, certainly, I see people whining when somebody fights smart to them there is still other kind of problems:
some one-trick pony classes that "ruin" gameplay for others.

A very simplified example:
Give one class "slay"
It would be smart for this class to use this ability and slay everybody.
People who play other combos may "whine" about it. You could say they shouldn't whine when somebody fighting smart with their chars (and the slay-guy does that), but there can be an actual issue to the gameplay that makes their "whining" legitimate. And the issue is that you either play a slay-class or be a loser.

Another point:
Sure, you can consider playing a sub-optimal combo and still try to win within self-imposed restrictions instead of whining. Plus you can actually set even more restrictions (RP, not using some armor, not practicing some skills).
And if you will look at a such guy through the article you've referred to without deep investigation, he may look like a scrub who is living in his world of self-constructed restrictions and thus by definition "not playing to win" and "not improving".
But it is not always true.