I think it is apt to call the weapons plastic, because they are in fact lacking any textures at all (they’re white by the default shader)–which is more matte than plastic. The point is, that is not metal, and the question becomes why make it so?
There is no subjectivity on whether it “looks like plastic” or not. It doesn’t look like metal. That is simply a fact. In fact, many new assets seem to not follow this principle anymore, like some Japanese weaponry featuring real metallic textures or the Varangian Axe. Compare for instance the sword Varangian uses (old asset) with their Axe. There is no subjectivity here.
They should retroactively fix old weapons to match the new. It just looks better. In fact, weapons in general need attention. As with the link above, there are many other examples of weapons that hit with the wrong side. Additionally, there are an incredible amount of errors with weapons in general. Rus Knights wielding a two handed poleaxe with one hand. English King doing the same with a Zweihander. All spearmen using the Guisarme (even ones from China).
Weapons in this game are a hot mess. That is a FACT. And it wouldn’t take a lot of effort at all to solve these issues.