Hearthstone Arena drafting is getting some changes. They are good changes, aimed toward a goal I approve of, but without knowing exact mechanics it is hard to say just how effective they will be.
The problem in Arena that they are trying to solve is that some classes are so much better than others. Mage and Rogue in particular are absolutely a tier above everything else and that is frustrating. I would like to play other classes regularly, but I hate selecting a class knowing it seriously penalizes my chances of winning and my card acquisition rate as a consequence.
There are two reasons for Mage/Rogue dominance. First off in Arena there is a real lack of AOE and other control resets. This means that the game revolves around minions beating each other up. Against most classes the ideal situation is you smash minions together so that the opponent's minion dies and yours is left with 1 health. This doesn't work well against Mage and Rogue, because they have by far the best hero powers for doing 1 damage. Against these two classes you can't effectively make awesome trades and they can, so they dominate the 'minion trading' part of the game, which is most of the game in Arena.
The second reason for Mage/Rogue dominance is just card quality. I think Mages in particular have it so good in this department - they have tons of common removal spells that are absolutely top tier. They have both multiple common AOE spells but also single target removal. Rogues get worse cards generally than mages but they still have a fantastic selection, better than other classes do.
Changing the first problem is a massive undertaking at the least. It would require a total overhaul of how Arena works, or a serious game redesign, both of which are things I think are not happening. However, changing card quality isn't actually that hard and doesn't need to do anything that would confuse a new or returning player.
Blizzard has decided that they want to move forward with this, so they are banning several top cards for Mage and Rogue and also banning a ton of terrible cards from weak classes. They correctly chose which classes were underperforming, and honestly the cards they are set to remove are mostly so terrible they saw little play anyway, so I think this is a good direction to go in. They can't get rid of the overpowered hero powers that Rogue and Mage have, but they can use careful banning to try to narrow the gap.
There is a real trick to this though. If those cards just vanish, then all the weak classes will end up with less cards to work with, and as such will be stuck more often with neutral cards. Neutral cards are weaker and less thematic so this is not ideal. It is still an improvement, but it isn't all it could be. If instead of just getting rid of the bad cards Blizzard added on an extra multiplier to the remaining class cards they could really make things better. So imagine that of 20 Priest cards 5 were removed. If they increased the occurrence rate of the remaining 15 cards by 33% then Priests would still get class cards at the same rate, but they would all be good ones instead of 1/4 of them being rubbish. This is a much more powerful change that would help maintain theme and increase the buffing effect of the banning.
However, given that Blizzard has said that right now they can only do on/off for cards, and can't subtly alter their rate of appearance, I suspect that they are stuck with the basic option which isn't as good. It will still help, but hopefully their tech improves over the next while and they can help even more.
I don't ask that classes be perfectly balanced in terms of win rate. These things shift with new releases and depend on who is playing, but right now it is so obvious that Mage/Rogue are the best that it feels sad to play other things. I don't want everything perfect, but I do want them in the same ballpark. It is a weird bit of balance - I don't mind individual drafts being wildly unbalanced, but I do mind class choice being that way. I think it is because I like to make all of my choices optimally, and if I play optimally right now I see only a small fraction of the cards and decks that are possible. If the classes were balanced I would win the same amount, but I would have much greater variety of decks and experiences while getting those wins, and that is highly appealing.