I think there need to be a couple banned cards in arena, namely Supernova and Quantum Towers. The problem with them is that people have decided that they'll just toss whatever the oracle card is into the same old rainbow deck because it can handle some dead cards. The result is that at least half the decks you play against are basically the same thing.
Wait -- on the one hand, people are complaining that Platinum is too hard -- and on the other, they're complaining that half the decks are virtual clones of one another? Dude -- build a counter to the clone army, improve your win percentage, share your counter with everybody, and watch as people move away from that archetype because it's not successful anymore.
Ta-da! let's use one problem to solve the other!
Except that won't really work. With an FG's boosted mark, denying them the entropy quanta to get going doesn't really work. You might be able to build a dedicated denial deck with some gravity nymphs, because they have enough SNs than BHs won't really phase them.
That last part of your comment is the design flaw in the arena, THE problem, that there are far too many copies of each card when a deck is duplicatedand when every card at 6 goes to 12. It doesnt matter what the player does he will get overrun or denied with almost no resistance.
There are a fixes to this imho. One Annoying and one easy.
1# The fix is that when you pick double draw dont duplicate the deck, simply force the use of 60-120 cards from your library before you can press submit. This of course requiters zanz to extend the deckbuilding window in the arena to accommodatemore more than the current 60.
2#
Keep the duplication and extra draw as it is and if you activated it, no more than 3 copies can be put in the deck, that way when the deck is duplicated there will be 6 copies in the final deck. The only exception would be the oracle card that would have 10 copies which seems fair and would make decks centered around what card you got. Now there wont be any, way too overpowered rushes I believe.