Singer also stated several times that Apocalypse had the
power of persuasion! I think one of Apocalypse's power was intended to be manipulation of emotions or possibly the increase emotions through his voice.
His voice obviously tied into these powers and was used in very artificial ways to imply how he manipulated his horsemen.
but
the movie never bothered to make this explicit and the ending was very absurd when Magneto and Storm simply walked away without anybody caring about their former despicable actions...especially Storm was horrible to watch. She did not show any emotions when her whole home city was destroyed by Apocalypse. All the children she lived together possibly killed but this woman did not gave a ratsass about it. Half-cocked things like that made this movie very painful to watch!