It's different online. Online someone else will actually do that work and probably small tournaments will run frequently, so there I think it matters enough that we should have 2-player rounds be the norm, and like I said, that is what I hope for and expect, but I haven't actually discussed this with Jay.
I think another difference between IRL and online is important: time. Consider the DS Tournament. Seven rounds of up to seven games each, nine games in the final. Now, online, seven games won't take more than two hours, and rarely more than 90 minutes. Less, of course, if it's first-to-four. IRL, seven two-player games could stretch to 3-4 hours including setup time. Qualifier rounds start to stretch for days. Even best-of-five is 2 hours per round, and most here on the boards would probably agree that a best-of-three match is not enough for a good test of skill.
Compare, say, the Catan qualifiers at Origins. (I can do this because I helped run them for three years. Yes, despite hating Catan). Around 32 people a day play for three days, four games, around eight hours a day. Each day is separate; the best one can do is to win all four games that day (maybe two people average per Origins), and most semifinalists had three wins and a good score based on closeness of games. This gets to 16 semifinalists. One semifinal and one final on Sunday. Note that all players basically get three separate shots at the semifinals, taking their best day.
What would a similar 2P Dominion qualifier look like? Thursday and Friday, N people play eight best-of-five matches (four per day). Top sixteen players go into Saturday, whittling down to two players by Saturday evening. Finals on Sunday. Great, OK... but...
For fairness, you probably go Swiss-style. The first two days Then you set up... 30? 40? 60? matches, with the requisite number of sets. You probably need at least four gophers just for setup. A perfect tournament uses the same five sets for each round, increasing the logistics. Seating the rounds takes 10 minutes. Slow play, a definite possibility, stretches those eight hours a day to the breaking point.
Is this a more skill-based tournament? Without a doubt. Is it a logisitcal nightmare? You bet your ass.
An IRL tournament will never be fully skill-based. It will be
skill-biased; a level 30 will beat a level 10 more often than not, but there's no time to figure out which is "more often," only time to figure which happens "this game." And that's "good enough." Most of the time. It's easy to claim that the Official World Tournament ought to be more skill-based than skill-biased, but the logistics are such that it can't and won't happen.
So, in that case, you
might as well have 3- or 4-player games for the tournament. More people can compete with fewer sets and less setup time.
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I personally think of Dominion as competitive only in 2P. I enjoy 3P and 4P at an actual table, but then, I don't usually compete when playing at an actual table... I play with friends. I rarely count cards. And I agree with Donald that 5P and 6P Dominion are... less than ideal. Much less than ideal, IMO.