I don't think this is a system issue, seeing as the only place he fits in a 4-2-3-1 is in the double pivot, which is largely the same as doing so in our current setup. His stamina/pace isn't quite up to what you'd want and it's noticeable in both formations. If anything he can at least play as one of the 10s under Amorim and potentially suits him better.
But yeah, his absolute 'ideal' position is probably something like the role Seedorf had in that mid-00s Milan team, where he contributes with nice touches, ball carrying and passes, but isn't expected to run the show. All we need to do is to find a Gattuso to put alongside him, a Kaka to put in front of him and a Pirlo to put behind him...