It's hard to expect an 8 cost minion that doesn't act immediately like Rag to see play.
Gruul has nice stats too, but he doesn't see the light of day.
Ysera?
You mean like a counter to Ysera. Ysera still gives you a card on the turn it's played, and has 12 health.
But Malygos drives home the point. You just can't allow that dragon to stay alive when played by a Rogue.
This new legendary can help clean up Kel'Thuzad's army, and it's something else that can pop up from Sneed's Old Shredder. But of course Sneed has the same problem brought up about 8 mana minions.
8+ mana minions that aren't game winners aren't looked upon highly in constructed. Still, the effect of this legendary is really strong if it gets off an attack.