He's Scott Carson for the 2020's.
Think back to when he was in goal - we even had a member say they hoped he came back with another team and kept a clean sheet, just to spite those of us who didn't think he was very good.
We can all see when we have a good keeper (Foster, Hoult) and all see when we have a bad one (too many to mention), but Johnstone occupies the inbetween - good enough for where we are, but not good enough for where we want to be.
If we want to move the team forward, we'll have to get rid. However I think the amount of money we paid for him will see us persevere until, like with Carson, he becomes a proven liability.