Playing mainly Aeon, I strongly disagree with your evaluation of selection deprioritizer. It serves at least 1 fundamental purpose : not lose your f***ing land scouts when moving your army of aurora or early labs ! The same can be said about shields going way faster than some other units and therefore not protecting them always, but I find this is less of a problem.
I do agree it adds a bit of micro to your play : you need to give scouts/shields an assist order, but once it becomes a habbit, i wouldn't qualify that as "taking too much apm/brain energy".
On the contrary, having to manually micro shields/scouts so they don't charge in their death is quite an apm-intensive process.
Now it may not be as relevant for other faction, or at lower level, but using this since I started ladder in May, I find it quite relevant.