Mitchell and the Roosters have the same dilemma as a number of good, relatively big ball runners, GI included.
Bird, Peachey (though not so big), and Dugan seem to have the same issue.
They are built like powerful centres, and have strong running games. In years past, they would all be centres (well actually forwards, probably lock forward going further back, but all players have gotten bigger since then and in the NRL era 80 kg centres are too small, mostly).
They are all great players, who could earn more from clubs valuing 5/8s and fullbacks more than centres, and they mostly have some football skills, without necessarily having the rounded skill set of an elite 5/8, or the short distance electric pace of the best full backs (though again, Peachey is pretty quick over short distances).
So they are all a bit in limbo in terms of starting position. They are too good to be paid an average centre wage, but not necessarily worth elite full back or 5/8 money (GI excepted, though his full back days are catching up with him).
I wonder if teams will continue to shunt their cap to the spine and try to mould these sorts of players in to spine players. Mitchell might be "bored" like Bird at centre, and maybe the hook was necessary to keep him interested in playing, or maybe it will make him wish to be a full back at another club.
There is no doubt he is an amazing player, but but at what position is he most likely to contribute?
It will be interesting to see what happens with Mitchell in the next few weeks, and long term.