They ARE toning down rng a lot. While i agree they could give certain discover and random gen effects specific cost parameters. (Renew should probably specify 1-4 cost priest spells, but sethekk veilweaver should add 5+ cost spells) this whole idea that you cant generate a card into a card is silly. Or cant generate expensive cards. Thats just bellyaching about a game you were probably losing anyway.
That kind of BS discover into discover plays have stolen games I would otherwise have won more times than I can count. Doesnt feel like your opponent outplayed you, feels like you just got scammed, hard. Its fine when it happens once in a while, but it happens way too often for comfort imo.
Never said you cant generate expensive cards, only that you should pay more for the chance to discover them, getting high cost stuff from 1-mana discover effects is broken, plain and simple.
But how did you get to be in that winning position all those times? Did you not discover any cards up to the point? Or were you playing a face aggro deck? In which case, I have zero sympathy, of course there are going to have to be some tools for slower decks to get an out in those games. Otherwise you just walk over your opponent and that's not healthy either. If you've had discover effects take the game away from you after you were in a winning position due to discover effects of your own, then you can't really complain.
From what you're saying, my first assumption would be that you're playing aggro demon hunter.
What exactly are these super big brain, skill required, no rng or discover decks that you seem to be playing?