I believe weapons are not really a niche. Generally there are a lot of weapons around. According to the last gctrader statistics, weapons are even a "poor performer" and the weapons category oversupplied. If this is true for any kind of weapon... I don't know. You may find this helpful: https://www.cgtrader.com/blog/low-poly-3d-models-vr-and-you-how-to-ride-the-wave-in-2016
Despite of that, I like your weapons (especially the plague doctor dagger https://www.cgtrader.com/3d-models/weapon-military/melee/plague-doctor-dagger-low-poly-an-material-ready) and hope people will buy them.
As for low poly, I think gctrader considers everything below 20'000 polygons as lowpoly (at least that's the limit for their low poly challenges if I remember correctly). But in the end it's a question of the model's purpose. I would say if the model is used in a game, 20'000 polygons can't be called low poly. And if the model is used in a mobile or VR game, 20'000 polygons would be clearly too much unless there is not much else in that game.
