With it now only working vs champs, the crazy sustain it offers for anyone who can gets crits is gone, which was the only real reason it was good. (and broken on yasuo, trynd, and panth.)
Every other mastery effectively only functions against champions, so it's no surprise that Riot took it that direction. Still, unlike damage, lifesteal's main function is sustain against minions, not champions. Warlord's will need some compensation, either through removing the cooldown, through increasing its numbers, or through letting the AS buff stack to 40%. Otherwise, it won't even be worth using on the champions it's currently broken on.
20% AS and situational, champion only lifesteal is nearly always weaker than 13.2 - 84.6 on-hit damage, especially considering most champions won't have enough crit to get it reliably until mid game.