i know when i am at home in track pants and a tee shirt just chillin, and i have to go outside, i will throw on a wool coat like that and its perfect. i dont need another warmer shirt to justify the coat going on, and without it, id be freezing. and from an aesthetic standpoint, the coat is not a duffle or something bulky, that looks odd over just a tee. its a pretty sleek coat that is not super thick, so visually, it does not look off over a tee.
so from both a practical and stylistic pov, i still see zero issue.