The campaign does really need an improvement since it's been the same from the start of Reloaded... Well, 1v1 was the same since the start of Reloaded while 2v2 and 3v3 were just gradual additions to the game as it grew from there... But you get my point.
As for the store, it's not gonna work out well while the transforming system is still a thing. I mean, think about it... If you have all of the legendary items on a storefront and are all purchasable, what's gonna stop a player from buying a powerful L-M and 5 bad legendaries in order to max that powerful L-M? Even if it costs tokens to get L-Ms or all legendaries in general, that would only mean that F2Ws are restricted from doing that while P2Ws can go all-out and just buy everything until they got full myth mechs with nothing but L-Ms.
Sure, it would alleviate all of the RnG gameplay of premium boxes, packs, and fortune boxes... But it'll cost F2Ws the small chance they have left to compete with P2Ws in arena if the legendary items are going to be in a shop for everyone to buy, regardless if the price tags are gold or tokens.
Legacy got away with the shop since items couldn't be transformed (they came in separate forms that had to be earned/bought) but with Reloaded, times have changed and we can't really afford to have another shop.