Two things can go wrong. Either your rotation, or the mechanics. If it's the mechanics, it's pretty easy to see where you screwed. And if it's your rotation, you just need to train againt Stone, Sky and Sea until you clear it easy. And none of this requires actual numbers. And again, I trained without a parser and ended with actual good numbers when I've been parsed in content.
I've done A1S as a tank and as a DPS. The two checks are nowhere on par. In every content if look at, tank rotation is set in stone. There is no randomness. It's basically why tanks pack the most attack power they can, and can stance dance that much.
Ok, then, tell me what you would do for such a DPS if you end with it in your party ? Will you look at its rotation during the fight, and tell him how and when he can improve ? Would you kick him, even with proper explanation, because he can't meet your requirement ?