I personally think Smith is more likely to be the 7th or 8th inning guy than Koji or Tazawa. The biggest problem is Farrell's mismanagement of the bullpen. I recall Jim Palmer during Orioles Red Sox games being highly critical of Farrell's handling of the pen, particularly Farrell having guys warming up needlessly and never bringing them into the game. This is one of the Orioles and Showalter's specialties managing the bullpen workload.
There is no question that the 2015 weak rotation early in the year contributed to burning out the pen. Nevertheless, Farrell has to do a better job managing when guys warm up and bringing guys into the game at the appropriate time.