my bad those are attachments with optics, not the optics themselves. but the point is still that each of these are differently positioned and sized (even shaped) so each of these will ‘clip through’ the weapon body in a different way, hence the need for a more robust system than vertex paint.
for multiplayer: this system is only relevant for the 1st person view meshes (the whole functionality should be disabled -except- for the currently controlled/viewed meshes from 1st person of the local client), so of course nothing the enemy does should have any impact on your own weapons, and of course you shouldn’t see clipping on the enemy weapons when you or the enemy does ADS. I thought that was immediately obvious but maybe I’m misunderstanding what makes it a problem in your eyes
a better solution won’t make the gameplay any better per se, but it would save time of setup and tweaking the positioning/sizing/aligning of the clip-through params in the material per-weapon per-attachment. you can focus more on gameplay if you save time on tedious/finnicky things 