As you may have imagined, I spend some time analyzing how sets sell. No matter what, inserting enough of a new set into the card pool that the playerbase at large starts finding good places for them takes time. Generally, this is only accelerated by injecting a lot of cards into the system. In the past, there has been a pretty basic pattern -- if the set has a lot of OP or at-first-glance-OP cards, a lot of people buy trying to get those cards and end up with all the others along the way. Since they have them, they start using them, and then others follow suit. The best way to ensure this is to lean some cards, probably rares, toward possible OP-ness. Not that I'm speaking for Japan, but you can see there are has always been a little bit of that going on during the MB days, when they were making the cards mostly themselves. The GP Sets, 10 and 11 (what about set 9? ER... yeah... don't worry about that one, it's almost always a bad example) were mostly designed by myself and the testers, but GP had its round of tweaks and comments, which were generally "are you sure this card is strong enough?"
Part of us at Apocoplay and the testing team wanting to make Set 12 our own was to NOT do this. Sort of set the stage for moar balance, less dirty tricks. Worry more about whether these cards will stand the test of time, add to the game experience as a whole, and be fun rather than make an initial splash and blow everything else away. This is probably the Card Set the Japanese had the least input on. At the same time, it borrows the most skills from the Japanese set. In other words, we more followed what they did and less what they said. One exception was that we weren't able to make many self suffcient decks in this one set like we did in 11 (although I think WK, maybe LV 4 WK is pretty close). We tried to squeeze a Crest AT buffer in but every time we did we made Lawt worse overall.
As expected, sales were slower. If you look at the sales rank of each set and the balanced status of each set, they pretty much line up in reverse order. Now we'll have to wait and see about the "stand the test of time" part.
"Scissors are overpowered. Rock is fine." -Paper