This is an alliance raid. That means 23 other players other than this AST, who chose to set down Earthly Star preemptively. If he/she did this expecting the tank would just pull, then the fault is their own. A pre-planned Earthly star is a coordinated effort, and in 24-man that type of coordination doesn't exist 99% of the time.

If I was the MT in this scenario, I still would've pulled prior to star going off, but not before saying, "WTF?!" I don't fault this AST for trying to optimize, but I will fault him/her for making a poor decision in an attempt to so. Optimization isn't just about maximizing damage; it's also about making the best decision according to the situation at hand. I bet there was still 2-4 players still catching up to the rest of the alliance (as usual), and that's why the MT was waiting.