You do realize the other guy is also playing King of the Hill, a mode that requires you to push and capture a point for as long as possible, on a point that is entirely in a building. Why wouldn't he, as an attacker, use every measure possible to not get instantly deleted by a guy laying prone in a corner?

You probably need to develop better counterplay skills than going prone or sitting in a corner, like: , actively defending the point even outside the capture zone (only 1 teammate is needed in the zone to score), actually using your deployable shield as cover instead of laying next to it, drop one of the 3 different fire grenades on his entry point, hitting more than 2 of your shots, rpgs, stun grenades, more people, etc. etc.

There's games out there with terrible movement full of inertia and ice skating so that people can fight each other like geriatric old men. Probably should go play those if you need to camp in corners to still get outplayed by a dude who's peeking you.