Per HSReplay, Spell Mage has favorable matchups against Control Warlock at literally every rank, from Bronze to top 1,000 Legend. This has nothing to do with tournament-level play. If you play Spell/No Minion Mage and consistently lose to Warlock, you are playing the deck wrong. Period.
And the idea that because a card makes you feel bad, it should be nerfed, regardless of its performance or popularity on ladder, is a bad approach to balancing. If a deck is actually problematic, it’ll show in either its winrate, playrate, or both. Control Warlock is a mediocre deck in terms of performance, and it has been losing popularity since the nerf patch came out.
Let me introduce you to Menagerie Priest. You can beat Control Warlocks as a control deck, as long as you have a proactive win condition. And if you don’t have fun watching a Warlock realize all their removal is still not enough to deal with your waves of Clowns, I don’t know what to tell ya. It’s great fun.