Just like others said Discover almost exclusively gives you neutral or cards from your class. One exception are for example the three tri-class Discover cards from Gadgetzan. 99% of Discover cards just pull from neutral or your class though. So I’m not sure what exactly you mean there.
And to be honest I would actually enjoy more stuff like the mixing of different classes. For example Witch’s Cauldron is one of my favorite cards. But of course I understand that some people like you don’t enjoy it that much for various reasons.
The best would be they make all sorts of cool cards and then give people a way to play how they want. For example if you don’t like Discover and every class should stick to their thing you make such a rule set. For even crazier Discover/RNG or mixing classes or who knows what it’s a different rule set. And then everyone looks for the “game table” they want to play on: