Off the top of my head Naismith, Griffiths, Martin and even Burke have all performed better without always even being good for Scotland than Mcburnie has.
Clearly going by club form none of these would be considered better players than Mcburnie but whether it's attitude or being ill suited to the formation/style of play Scotland uses something seems to be stopping him from getting close to replicating his Sheff Utd or Swansea form. Hopefully he comes good but the idea of not using his previous form for the national team as a factor in whether he should be picked or not seems unwise.