Blizzard
I think it's cool we decided to share some data there, but overall class win rate doesn't really share the best story when talking about balance or design goals. We mainly look at archetype reports and check out whether or not each class has at least 1-2 strategies they can look to to be successful. If that's not the case then we try to either bump existing strategies or create new ones. For EX: at one point Rogue was around 43% win rate, but that was largely because so many people found Gang Up / Mill to be something they enjoyed playing. I think most people that made the deck went into it knowing they weren't playing a hyper-competitive deck, but did so anyway because that archetype was fun to them. The chunk of players playing Gang-Up Mill drove Rogues win-rate down a ton, but that doesn't necessarily demand a response of 'the win-rate of Rogue is low, they need stronger cards to bump up over 50%'. There are many examples similar to this. In any case, there is no one happy when a class does not have a fun/effective strategy they can turn to. If that ends up being the case with any class we are looking to try and fix that, whether it's a perception problem or an actual one doesn't really matter.
Blizzard
We've had similar articles in the past about design stories for particular cards, I think the most recent one I remember discussed all the design iterations that Yogg went through. Card designs have a number of different goals, sometimes those goals are immediate competitive play and sometimes they shoot for something else. Things like flavor, arena viability, or sprinkling in tools for a new or existing archetype. In smaller sets, it can be a little risky to take a gamble on a new toolkit because there are fewer cards to work with. In the case of Priest, we were pretty happy with the amount of options the class was getting from neutral (Barnes, Curator*, Medivh, Dragon Cards) to do some testing with a new archetype that Purify could be a part of. In my mind there is some positive to the outcry over Purify because I think people will definitely try it out and report any successes/failures/stories they had building and playing a 'silence your own stuff' priest. None of this is to say anyone is wrong in their feedback, but just to communicate some of the ideas surrounding a card design. Hearthstone is important to all of us, and we're trying to do better in terms of communication and understanding what different communities (like this one) are most interested in. I've been happy to be here and have a conversation about what you all want from the game, thanks for being so passionate about it. :D
Blizzard
Specifically for PriestFeast I think it has the potential to be a bigger swing that it's credited for. 3/6 is hard to deal with and Priest has access to a number of spells to make the trigger happen. Drawing and combo'ing with 2-3 spells on T7-8 can push you completely out of range of a lethal from an aggressive deck and swing you into late-game where you have a large advantage. Been fairly solid in playtesting as just a card to play on curve.
Blizzard
Charge cards are a little tricky in that every time we make one players find out the best way to use them is to hold them waiting to combo other cards to deal 15+ damage from hand. Not something we get super excited about ;).
That said, Charge has some cool flavor and feels very Warcraft universe to me. Finding designs for Charge that don't result in mass damage from hand I think is something we'll do in the future. As far as Windfury goes, I don't think there is much preventing us from going there... but is does feel very Shaman as a mechanic and I think we've just been more interested in exploring different designs/mechanics for Shaman than going back to Windfury in the last couple sets.