Clearly they are 2 very different styles of 9,s. Roby is very quick out of dummy half and is very effective at getting teams on the back foot, and needs a lot of push from teammates. MM imo jumps and attracts the BM and A only and has runners and 2,s plays and Wigan play of the back of this with to get the ball to the edge quickly.
I would play them both, at some stage of the game. Having Borrows at 9 is the same style as Roby but no where near as effective. I also agree that scooting without support looks good, but without another QPTB to get out to an edge may as well be a forward drive.
IMO Roby is a quality player who I would love to see in a Wigan shirt, but MM is also getting there. He defo should have been on the bench, he,s a very honest, hard hitting 9 he will only get better.
Cameron Smith is not know for quick scooting from 9, but organising well and gets the pack going forward and the Aussies then play of the back of this with their outside backs.
Play them both, if one styles not working we have a plan B.
Just an opinion