The whole creating a black hole in Thanos's brain seems a lot like the argument that Dr. Manhattan could demolecularize someone like Thor or Superman. Just because he can control molecules and Superman is made of molecules, doesn't mean he can do so to someone with Superman's durability. Same here with Thanos. There's ZERO proof a black hole could be made in Thanos's brain....especially by someone who is CLEARLY on a lower power level tier than him.