How the change on the core set would fix a lot of hearthstone problems

TL;DR: Creating a new core set using past expansion will largely increase deck building.

I have this idea that I want to share with the community. I think that pretty much everyone agrees that the problem of class imbalance is rooted on the core and basic sets imbalance. Paladin needed 3 expansions to become good (and with MC even too much good), and when naxx and GVG rotated out, paladin has gone back to the dark. Same for priest without lightbomb. Warrior, druid and hunter has a very solid basic set, and with every expansion they can find replacement for cards that rotate out and keep their identity.

Some class start with a great advantage each rotation, and if very powerful, meta shaping cards are not printed, the other class will always strive to keep up. The attempt to make shaman viable, for example, generated a deck which everybody agrees to be too strong, and the same happened in the past with paladin. Some classic tools are too strong. Why hunter has to have a useless legendary, while paladin has tyrion? This is counterbalanced by very good cards for the hunter (Savannah Highmane or Houndmaster), but this only make the problem much more complicated. Because of Savannah, the hunter will not have any good legendary, probably.

There is another problem that I see with the core set. Many cards in the core set are quite boring, and the coolest card are in the expansions, that eventually will rotate out. Reno Jackson and Grim Patron are good example. They have interesting mechanics and if properly balanced create the most interesting decks to play. Why I should have King Mukla always available as a possible choice for my standard deck, and not Reno?

Finally, some interesting cards will never see competitive play because they lack of synergy and will eventually rotate out before a good deck can be build around them. For example gorilla bot is pretty much useless with most of the mech gone. Another aspect of this problem is that some cards will never been played because their niche is already taken by a better classic card. Flame juggler, for example, was almost never played over Knife juggler, before the nerf. And if a something better is created in one new set, when this set will rotate out, the classic card will take back its role (for example Cairne). This make deck building and playing much less interesting because you always see the same card to be played.

My suggestions to solve this issue is to change completely how the core set works. The core set should be a combination of several old expansions, instead of being composed by classic (+the "core" that is now obtained by leveling the character). So at the new rotation, the core set can be created by a subset of classic, gvg, tgt, naxx, brm. Overperforming cards has not to be part of the core set, but also very bad cards, that do not have any synergy (so no doctor boom, and hemet). I personally would also change some stable card class (savannah highmane, fireball, innervate, warrior axe etc) because they define too much what a class is, and do not leave any space for experimentation, but this is my personal point of view.

In the game shop, instead of selling classic packs blizzard should sell core set packs, that can contain any card that compose the core set for that year.

The developer has stated that the reason for keeping the classic, as a core set, is to give the opportunity to returning people to have a solid start, instead of starting from scratch each year. This can still be achieved by removing the cards from the core set very slowly each year. For example, if a single card is meta defining (misterious challange, grimp patron, etc), it can simply be removed for the next year (or maybe faster, at next expansion release), think now the shaman without 4 mana 7/7. It could still be viable perhaps, but surely not as OP as now.

Hope to have some feedback on my idea!