You can believe whatever you want, but you compare completly two different mechanics (cone and all-aware). Sure it was wasted in XCOM because you couldn’t designate an Overwatch area and the very first sectoid to move was screwed regardless of being not important.
Yet still, let’s look how it is done in XCOM2…
It is sequential, but at least enemies don’t move while your soldies take turns. And that is one of the solutions I am asking for. But fuck, better to have something uterly stupid because someone somewhere else once also did something uterly stupid. 
One could ask, why can’t we have things that are not uterly stupid? And so I am asking…