In today's tournament, I found that there was very little, if any, metagame. In a tournamnet without a metagame, there is one best deck that can win more than 50% of the time against every possible deck.
Rulesets like this usually aren't a problem; they allow good deckbuilders to not have to worry about prediction and instead win by having a stronger or more optimized deck. Unfortunately, in these tournaments, deck-copying can be a major problem.
In a tournament with a distinct metagame, if the opponent copies your deck after Game 1, you can prepare and counter it. This isn't the case in a tournament with a small or no metagame. In a tournament without a clear metagame, if the opponent copies your deck after Game 1, there is no way to counter them if you were using the best deck in Game 1, which is clearly the best strategy. Games 2 and 3 will be purely luck. I don't think tournaments should involve pure luck for Game 2 and 3.
In tournaments without a metagame, or with a very small metagame, I think deck switching should not be allowed. This would cause these tournaments to be mostly deckbuilding skill with some luck involved, instead of mostly luck with some deckbuilding skill involed. Besides, there isn't any need for the best players to switch decks if one deck can beat everything else more than 50% of the time.