How do historians think about the portrayal of Mozart in Amadeus?

This is a tough question to answer in a way that meets the standards of AskHistorians, since it's not going to rely much on scholarship and will have to rely more on anecdotal evidence. But as a student in musicology, I can give a sense of what historians think about the film, which will of course vary substantially from person to person.

Historians generally recognize the film for what it is: historical fiction that reinscribes certain "myths" about Mozart, but does get some things right and is generally successful at balancing history and entertainment.

The specific myth it inscribes is that of "the eternal child" (see Maynard Solomon's biography), which is a Romantic myth of Mozart that exaggerates various immature aspects of his personality and paints him as this sort of unknowing vessel of divine inspiration. Generally, this is coupled with a view of Mozart's music that emphasizes "formal perfection," "heavenly beauty," and focuses a good amount of attention on "dark" pieces such as Don Giovanni and the Requiem, as instances where the psychological distress that comes from not having a childhood and having an overbearing father bubble up to the surface. It's a very similar myth to the one we've constructed about Michael Jackson's personality. It's one way that people have been able to advertise Mozart's music to a crowd that tends to adapt a more romantic sensibility.

It's not that he wasn't immature, that he didn't have an overbearing father, that Don Giovanni doesn't have some dark undertones, or that his music isn't gorgeous. It's just that this myth emphasizes those elements of his personhood and output to the exclusion of most other elements. But that's the thing about historical fiction, you always have to do that. You always have to either use an existing and popular myth or construct a new one out of biographical materials. So the fact that Amadeus did that isn't that big of a deal.

But what other myths could have been constructed? To answer that question, I think we have to investigate Amadeus's biggest "victim." Musical culture in the eighteenth century more generally.

You see, the "Eternal Child" is fundamentally a romantic vision. The artist, as a vessel of divine inspiration, creates perfect art for perfect art's sake, he is fundamentally misunderstood by his contemporaries, but he persists against all odds for the sake of art itself. The audience needs to rise to his level, not the other way around. The film portrays the musical culture of the time as eternally locked in combat with Mozart the genius: from Joseph's "Too many notes," to the political schemes of Salieri and the other composers at court. We are meant to scoff at these, we are meant to view these incidents as the uninformed prattling of dillettantes who fundamentally misunderstand Mozart's artistic vision. The culture is always against Mozart, the movie defines his genius as that which is greater than his contemporaries could understand.

Recently, a new vision of Mozart has emerged (itself, of course, also inevitably a myth) as a master craftsman, one of several master craftsmen working in Vienna at the time. This vision emphasizes the communicative aspect of Mozart's style, emphasizes a robust tradition of compositional training over divine inspiration (recasting the role of Mozart's father in his youth), downplays the "bildungsroman" vision of the importance of childhood as a period of growth (since it was really the lot of craftsmen in general in this period to not have a childhood, see the many who were recruited into conservatories or castrated to become singers at an absurdly young age), views the musician as constantly in a state where he has to cast his products in terms that his audience understands, emphasizes the competition inherent in any marketplace, and thus fundamentally would view 18th century culture as an essential part of what Mozart's music was. This vision would cast Mozart not in opposition to his culture, but fundamentally working with it as a discourse that enabled his artistic products in a positive sense. We would understand that Mozart would want to tailor his compositions to suit his performers and touch the heart of his patrons, rather than view both as know-nothings that stand between the artist and his divinely inspired vision. Such a myth would not necessarily view Mozart's immaturity as at odds with his products, since we don't tend to observe a strong link between artisanal craft and personality (as Gjerdingen points out, we would never think of a tart dish as indicative of a cook's "tartness," see his Music in the Galant Style).

At the end of the day, every single biopic has to select a myth on which to base its historical depiction. The vision of Mozart that Amadeus promotes is a well-worn one that was popularized in the 19th century and remains popular to this day. It's a relatively safe vision that helps those with romantic sensibilities to appreciate Mozart's work. But I do think it would be interesting to observe a biopic based on a non-romantic myth. But perhaps the romanticism inherent in the biopic as a genre would prevent that from coming to be.