I don't think that Colwill can cover the ground that Doyle can. Colwill probably has that little bit more quality in the final third but he is nowhere near Doyle in terms of work rate and defensive duties. Doyle off the ball presses like a demon. Colwill is a big lad, covering ground isn't his game in my opinion. For colwill to prosper then he needs to be in that position where he is allowed to link up attack and follow his passes.