Go back and read what I wrote, because you are blatantly ignoring that "ally-only" and "enemy only" are conditions separate from oil slick arrow's. Sorcery's enflame is actually more versatile because it has a function vs allies or enemies. Now, if they added an additional effect to oil slick arrow, where it did something different if it were hit with cold, negative energy, smashing, lethal, or psi, then maybe you'd have a point. You cannot take poison, as a MM, without having access to henchmen. In fact, they modified the set for ATs that don't have them. If they didn't, then again you'd have a point. You don't need to go outside of your primary for that, either.