Actually it doesn't. It clearly states "a player who is handicapped by self-imposed rules". A self-imposed rule is for this matter "I won't ask other players to use a specific type of gear."
I also do not like the d/d backstab thief and play a high tirckery build nothing wrong with that.
But let me quote once again what you have clearly missed: "The first step in becoming a top player is the realization that playing to win means doing whatever most increases your chances of winning. That is true by definition of playing to win." Because winning does not only mean "getting a task done" but also "getting it done as fast as possible" the definition is quite correct. For example: Is everyone who is able to sprint 100m a winner or only the one to arrive first? Also this is not my definition but the one of David Sirlin.
Okay, post got eaten because I pressed the back button on my mouse, so this'll be somewhat short.
I don't know Sirlin, but his definition of 'playing to win' is false, because his definition of 'winning' is off. Winning is achieving victory. As long as you try your damn hardest to achieve victory, you're playing to win. It doesn't matter if you lay further handicaps on yourself and your party.
How do you 'win' in PvE? By beating the dungeon. It doesn't matter how fast, or if you do it with a 0/0/0/0 build and only grey gear. As long as you eventually beat the dungeon, you win. Saying it needs to be done fast and efficiently, or without forcing people into an optimal build are all just conditions which you pose onto yourself and/or your party, each of which being completely unrelated of whether you 'play to win' or not.
There is nothing wrong with doing this, not at all. Just like there isn't anything wrong with running a mile in an hour. However, it isn't really "winning" it is just competing at that point. Anyone can complete a dungeon. Doing it fast and efficiently is often more of a win condition than just completion - at least given the ease with which people can complete content/dungeons in this game.
Yes, dungeons are quite easy, but that doesn't mean the win condition changes. Even if you're running against comatose quadriplegics, you still win as long as you finish before the others do.
Except I haven't been raging against the OP for a while now. I still think it goes against the idea of the pugging system, but I can accept it if you actually tell people about it beforehand. What I have been raging about is those people who say that they kick others when making a mistake, which segregates the playerbase and makes upwards mobility on the skill ladder much harder, since you get kicked or blocked from games because you're not able to learn due to that kicking and/or blocking.