I agree that Barker needs to add more end product and goals to his game - and get as frustrated as everyone else as he seems to have talent.

One thing that he does though, is have a reputation for speed (like Boyle) and what happens in many games is that teams try to double (or treble) up on him - this creates space for the midfield / strikers.

e.g. Murrays goal v Hearts

https://www.youtube.com/watch?v=tocdHvN1gd0