You could argue the same thing about Ysera because you're not going to get the dream card until the end of your turn. Sub in whatever legendaries you want. This is a really simple, straight forward boss taht doesn't need a perfectly optimized deck.
I had to sub Troggzor and Geddon because I didn't have them for Sylvanas and a Sea Giant and beat it in one try. IMO, Sylvanas is really good for the matchup because he'll almost always have minions in play and loves to Brawl.
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haha he is a very fun guy, 6 mana which is not equal to 7 mana.