It's also identified as a neo-noir in its own Wikipedia entry--which I would think constitutes a reasonably mainstream endorsement of your assertion.
I haven't seen it in thirty years, I must admit, but it is on Amazon Prime, so I'll work it into the viewing schedule in the near term just so I can get back up to speed on the details--my recollection was that it was spooky as hell, however, and that its scariness (much of it derived from the malevolent presence of Robert DeNiro, who reportedly creeped out director Alan Parker so much that Parker let DeNiro direct his own scenes!) may have caused some folks to push it over into the horror genre.
I think it's a question that should get directed toward Eddie Muller, as it would push past some of the more stilted discussions that come up in his "Noir or Not?" feature. IIRC the film pushes the line in terms of sexual content, but I think it should be considered for a TCM slot in a series that could be called "Neo-Noir or Not? Dark Films That Push the Envelope." (They could screen it in the wee hours, as they do with some of their other, edgier content.)
FWIW, prolific German noir writer Matthias von Merkelbach, whose work has been plugged by Eddie, is high on ANGEL HEART, considering it a neo-noir and giving it 4 stars out of 5.