is it a bad thing that the weapons have high poly, such as laging the game massively or anything like that?
I wouldn't say much about the lag, since it varies so much, but it's extremely out of style. It's like putting Battlefield 4 models in Minecraft. Overexagerating, but it's the same principle.
It works, and the gun is of quality.
But it shouldn't be made, at least not for the prior title.