PI is on the Priest tree, not the spec tree. All Priests have PI, and in fact the Priests involved in that kill did all have it chosen. You don't seem to know these things very well, perhaps you are not in a great position to evaluate this kind of thing properly?
Yes. THAT'S THE POINT. People are AFRAID of this, no one can say what'll ACTUALLY be the case because the spec isn't available on live yet. Anything could change by the time it goes live, but people are pointing out there's the POTENTIAL for problems. Big ones.
First off, you're already defusing your own argument here because they CAN control who gets the buff by positioning.
Secondly, you seem to focus exclusively on their main-stat buff, but that's NOT the only way Augmentation increases people's damage. It's just one of them, and the simplest one since it's fairly automatic given the extension mechanic. It's very different for the others.
Stacking effects like Prescience + Fate Mirror and Breath of Eons are the biggest culprit because it creates burst windows where buffs compound each other. Properly stacking these effects is going to make for WILD damage swings if executed properly. And again, no one knows the exact numbers yet because it's not released, but this kind of playstyle creates the POTENTIAL for problems. That's all people are pointing out.