I feel quite the opposite. Song Shield only affected a target after being affected by a crescendo. That means you used your big heal, and now you’re protecting for a small portion of the next hit. That didn’t really come into any rotations in end-game with any of the Bards I talked to.
We had several Bards on Crypt 15s yesterday who used Instrument of Protection and found it far more preferable than Song Shield, especially because Song Shield would have negated the Encouraging Note.