Why was Tom Hulce (Mozart) nominated for Best Actor and not Supporting for Amadeus?

I was rewatching Amadeus recently and the more I think about it, the more I’m convinced that Tom Hulce being nominated for Best Actor instead of Supporting was a weird move. It basically forced the two leads to cancel each other out, even though F. Murray Abraham ended up winning. My main argument behind this thought is that Salieri is the undisputed protagonist of the movie. The entire story is literally told through his perspective, his confession, and his obsession. He is the lens through which we see every single event unfold. Even though the movie is named after Amadeus, Mozart feels more like a *force of nature* that the actual protagonist reacts to. If you look at the structure, Mozart is really a supporting actor who is there to react to what Salieri does. In the beginning, we don't follow Mozart’s journey to the court, we follow Salieri meeting him. We see Mozart become the top composer in Vienna specifically through Salieri’s eyes and his jealousy. Even the parts where Mozart is more involved, like the father and son montage, it’s still framed as a reaction to the plans Salieri is setting in motion. Salieri is the one driving the plot and making the choices, while Mozart is just existing and creating, unaware of the trap being set for him. To me, a lead actor is the one who tells the story and moves the events forward. That is 100% Salieri. Mozart is who the story is about, but he isn't the one through which the story is told. What do you guys think? If Hulce had been put in the Supporting category, do you think he would have won too, or was his performance just too big to be considered a supporting role?