One thing that I see that hasn't been fully mentioned, though, is that the mono deck, duo deck, etc sections and rules governing them are aesthetics, no one can really dispute that accurately. So yes, that isn't so great when you can concentrate on the gameplay mechanics and build great decks that use whatever cards you want. But, it is said here, talking about themes and such, the deck sections follow this perfectly. No one is really trying to force mechanics into the deck section, because the deck section is basically 60% aesthetics, 40% mechanics. Decks are built under the rules of a certain deck aesthetic and then mechanics are built around that to make the deck function. So, I guess I don't understand why people were getting their panties in such a fit back on other threads. Sure, no one really mentioned that aesthetics were a main part of it, instead, shots were taken at the idea of aesthetics. That was all rather stupid.
That being said and going somewhat off topic from my previous paragraph, Aesthetics are important, very important actually. While yes, the gameplay mechanics are what really make a game good and playable, without good, or at least decent, aesthetics, the demographic sort of goes out the window, the eye grabbing factor that makes you suddenly interested in a game go away, and that all hurts the value of a game. If the newest FF game has old school 8bit graphics, but brand new mechanics, mechanics that would eventually change the gaming world as we know it, do you think that game would really be so popular? It might for some people like me or jmizz who played the old school graphics and know just how awesome they are, but to newer generations, aesthetics are extremely important.
I know where I went with that paragraph kind of goes parallel to this thread and not exactly a response to it, i was just making a note. Mechanics are great, and that's the kind of person I am, but that being said, without some kind of aesthetics that appeals to my eye, I will probably glance over the game until I one day come across a glorious review of it.
tl;dr: The deck sections focus on aesthetics, as they are there to have decks that fall under their theme. Aesthetics are important to bring in new people to a game, but without good mechanics, good aesthetics are pointless.