Or you could just name with the Therapy one of the one or two cards that can beat you in the current situation and keep your board intact.
That's the other half of my point. By the time you Dread Return a Hypnotist, most of the cards in your opponent's hand are probably irrelevant. And most of the cards that are relevant cost zero or one mana, so he's probably not holding them back for you to discard. Unless you're Dread Returning and using Sadistic Hypnotist before your opponent takes a turn, they're probably going to play most of their relevant cards on their first turn.
Countermagic is relevant when you're trying to resolve a Dread Return, but since you need to resolve one to get a Hypnotist, he's not really better in the face of countermagic.
Crypts, Relics, and Explosives get played on the first turn or as soon as they're drawn. Hypnotist isn't really useful against these cards unless he's in play before your opponent has a chance to resolve them.
White removal is relevant, but also instant speed and costs one mana. And if they're holding one with an open white mana, you're only going to be able to discard two cards with Hypnotist at most.
Your opponent's creatures are usually irrelevant since you make more creatures faster. Creatures like Mogg Fanatic that can remove Bridges on a whim usually cost one mana.
I guess he's good against stuff like Pernicious Deed, Firespout, and Wrath of God. But these cards are easy to play around --- just keep a few non-token creatures around to rebuild your army.
I don't see how Sadistic Hypnotist is really useful unless he's coming down turn one or two in a situation where you can't just win. There are so few cards that are actually relevant against us. I've been happy with just Cabal Therapy and Unmask to remove problem cards while the rest of their hand sits there uselessly against a horde of zombies.
That's how I feel about Hypnotist. Flame-Kin Zealot and Eternal Witness/Sphinx of Lost Truths allow you to win without quotation marks.

