I will admit that it may be time for the Skins and Cooley to part ways but only from a cap and health stand point.
Your other arguments could not be more wrong. Cooley has always (when not injured) been a yards after the catch guy. He has been known as a guy that doesn't go down on the first contact. As far as throwing down the field, Cooley was Fred Davis before Fred Davis got here. That is to say Cooley was the hybid tight end that could stretch the field. As for blocking, Cooley is not the biggest guy and by no means blocks like a lineman but has been a way above average blocker throughout his time with the Skins. Hell they used his at fullback to block at one point.
Let's not try to re-write history to try to justify getting rid of someone that was at his peak one of the most valuable players on the team.