I would say it is a “fashion” jacket in the sense that they are very high profile among the more trendy set and with lots of product placement etc, rather than using “fashion” in a negative sense per se - I would bet that on asking a random sample of high street shoppers in London or another fashion-conscious big city to name a quality leather jacket brand most of them would namecheck Belstaff close to the top of the list but very few if any would mention Aero, Vanson, or even Lewis - and yet on FL the former barely get a look-in….so although seemingly not very fashionable on FL, there is no doubt they are very much so in the wider world. What intrigues me is why the disparity? As Monitor says some of their leathers are very good, but in my experience it varies wildly with the era and models - and many of the jackets I have handled recently have certainly been below the standard of the regular makers on FL but also at a higher pricepoint, making them poorer value for money (for me at least). I also agree many of their older moto designs were excellent - the same for their classic wax jackets - and they have rebooted the moto line in recent years, so it might be worth another closer look. I do find the fits generally very weird though, but that might just be me! Many of the instore jackets seem to have incredibly narrow chests and very long arms - and given there is no m2m option getting one tailored to fit puts them into an even higher price bracket….my general feeling is if you want a lightweight smart looking jacket they are a reasonable bet, if you can get the fit right and don't mind paying extra for the badge - but for something more substantial, I would look elsewhere first these days….I think it's an excellent looking jacket and having owned & wore a few Belstaff jackets, other than the lighter leather, I wouldn't place them behind any of the makers you've listed. Strictly visually speaking, leather on a good Belstaff jacket is on a level that our favorite makers have yet to reach.
Their 80's to 90's motorcycle stuff is very impressive, too.
As for it being a fashion jacket. . . Since this is something dictated by the purpose of the jacket, I think all of our jackets here could be classified as fashion pieces.