I think the duel mode is really interesting, and I know that there are a lot of changes that will no doubt be rolled out in the weeks/months to come. That said, it really seems like robes of gaudiness are going to be a huge problem in their current state due to how oppressive they are in the mode. Sure, you need to make a deck that can work with them, but if you choose to start with a paladin or warrior with some heavy cards you get to shutout the game by turn 4.
If you are going to have a mode that is PvP you can’t have this level of ‘cheating’. Perhaps every third card could be halved so the players building these decks would still need to run smaller cards in order to get to their mana cheating. There already is the passive that allows 6+ cost to all be reduced to 5 mana, which still allows the other player time to get to play their deck.
Maybe the dev teams data says otherwise, but when watching streams or playing games myself, it seems like you get your runs stolen by this passive; which is decidedly not fun.