I don't think it's really that insane. There's so many meh (Nat Pagle) or outright bad legendary minions (Millhouse MANASTORM!) that it's a total crapshoot. It's fun sure, but it's likely going to be generally worse than Medivh, as you get 3 free minion summons with him (rather than 2 minions added to your hand you'll have to pay mana to play) and you have some control over which ones you get from the staff via the cost of the spells you cast. Obviously, the fact that it's random is going to mean it's going to high-roll and win the game sometimes, but like Yogg, there's going to be no consistency to it.