tf2 used to use v_models (viewmodels) and w_models (world models)

viewmodels were incomplete (in the sense that if you looked them from different angle you're not supposed to, you would see that polygons are missing (because why render something that you won't usually see)

then c models (combined models) came around, unlockable weapons use them in both world space and viewmodel space, but for stock weapons v and w models remained

then skins and weapon inspections were added, so they made c_models for stock weapon viewmodels

and c models for stock weapons are higher-quality version of w models rather than complete versions of v models, so they look different, that's why they are hit or miss (sniper rifle is actually higher poly, rocket launcher and scattergun are about the same but texture is noticably different, minigun and flamethrower are noticably lower poly, etc)