Salieri in Amadeus

[Alex K]

Any perception of Salieri as incompetent is expressive of his own sense of inadequacy in the face of Mozart's innate genius, his "God given" talents provoke not just jealousy but a full existential crisis in Salieri, he witnesses Mozart's genius and sees God's contempt for him, he adores Mozart's work so that it fills him with resentment for his own perceived inadequacies. The sense that Salieri is a failure or an incompetent is subtle character development, put forth by Salieri himself, the one telling the story.

I see what you mean, but I do not entirely agree - in the scene I linked above, Salieri apparently struggles desperately to write a simple and pretty pathetic "welcome march" which Mozart then spontaneously improvises into an Aria. This objectively portays Salieri as unrealistically incompetent.