To me he'll never become a talent of the very very top level, but that's ok cause you can't have every position covered that way, he can still be an excellent player who contributes well to the team.
He should be more box to box free to move around with a properly solid DM behind him, tackling and working in midfield without quite the same demand for positioning, and free to get to the edge of the box to make the most of his great long shooting. I think the Leeds game showed that best of what he can do and what I want to see of him. Other teams won't leave such huge gaps like that specific case but if he gets forward more regularly like that presenting a threat it frees up space for the rest of the team, and runs from deep are hard to track even when teams are looking for it.
The duo with Fred makes him always less than his best ability.
I thought earlier in his career he could be molded to a DM, but either they never really tried, or they found it wouldn't work.
Similar to how Lindelöf and Maguire even with regular play to get understanding and consistency going will only each play to 90%(probably less) of what they could do with a more complementary player even if their form is at their very best. Both need a quicker player beside them (especially Maguire though).