I don't disagree with any of that but the big unknowns are can he be a coached to think, and can he be coached to give a fudge? If he can, £20-25M is a steal, if he can't we'll have tinkled it up the wall.
The following data are a year out of date but I don't have the up to date versions. The following image points it out quite clearly:
He's clearly got the ability, but no brain. I don't know if he's just too dumb to learn (Walcott) or in need of the right manager (Rose). Like I said, I guess it depends on your risk profile - I think more than £20-25M is too much risk given that various managers have yet to coach that side of his game. Given the way Poch clearly expects the team to play, the tackles/interceptions figure is concerning.
Another interesting bit of data from that season, the average progression towards goal from Barkley's possession in that season was -1.06m. In that same season, Deulofeu managed +3.65m and even Gareth Barry achieved +2.85m.