He's perfect for Allen. Allen craves that critique of his performance and Diggs doesn't hesitate to provide it. What got Diggs run out of Arizona by Cousins is what makes him perfect for Josh.
Amazing trade btw, way better than anything you could get in the 1st round. You'd hope that a drafted receive could become a #1 on the level of Diggs. The price was pretty low and only got overshadowed because BoB was gonna teach Hopkins a lesson (which seems to be really working out for BoB btw).