A jacket that fits everywhere else but sits wrong at the shoulder still reads as ill-fitting, because the eye checks the shoulder first and only forgives the rest if that line is right.
Soft-shouldered, unstructured construction isn't a style preference so much as an admission: most rooms this jacket will actually be worn in are not air-conditioned enough for heavy canvas and padding to be worth it.
Try a jacket on and roll the shoulder forward slightly, the way you would reaching for something. Structured shoulders fight that movement. A good unstructured one simply follows it.
