The idea of getting the computer to play itself in order to test answer the question, “Which deck is better?” is very difficult. Even if you could create an AI good enough, what would it matter if one deck always won? If you wanted to play the deck in a tournament you would have to learn how to play the deck yourself, which would be complicated.
I don’t think computer vs. computer games are interesting or even possible. One, you have to program a great AI. I think writing a good AI is possible, but a tournament winner would require the computer to use the sideboard also, which seems impossible to me. Two, you would have to implement all of the cards for a couple of blocks, which is about 1000+ cards and have them all work correctly.
Three, watching the computer play itself is boring. I think everyone would agree that playing Magic is more fun that watching Magic. The idea of the computer playing against itself is theoretically interesting, much like a chess program that plays itself, but in reality it wouldn’t mean much. Tournaments have a decent amount of luck involved even if you are piloting the best deck, since you are paired against other random decks which would increase/decrease your chances of winning that match.