I think there is a misunderstanding: Dota doesn't apply to the quote "Game developers should create a well-defined concept ..." since it was neither conceptualized nor made by the Warcraft programmers.

Additionally, the originally Dota started as a mod, was then published as a game, and Dota 2 would then not count as a mod. Its not hard to come up with a definitive answer to that. A game is a mod if it doesn't stand alone, if it requires _modifying_ the structure/code of another game.