Rather than tradition, don't you think it's about when Luke's experience/Roache's zip have maximum effect?
Oh absolutely. Well thats kind of what I was getting at when I said this below in my post you just replied to...
I guess Kearney can just experiment...Or he can dig deep into his coaching prowess and field which ever according to the other teams style, horses for courses so to speak.
Back to the tradition thing and to your good question - Luke has been no stranger to opening up games before the less experienced comes on to sub him. McGuire at Souths use to open with Luke and then bring on guys like Nathan Peats and Apisai Koroisau and to very good effect. You see heaps of clubs do it like the Broncos with with McCullough and Nikorima when Bennett was using Nikorima as a hooker.
Obviously one of the advantages of bringing in your younger, quicker guys, is to take advantage of tired defences. Particularly the big men that make up the middle thirds. Roach has a fair bit of acceleration in him and has shown in the past an ability to break the line. Roach also brings experience in the outside backs that he can cover for.
Jazz is along the lines of your Keiron Cunnigham/Brandon Smith somatotype hookers but he's not as good. Not right now anyway. Jazz does have the right attitude and potential. I just don't think he's there yet but probably just needs more first grade games.