You are missing the point. It's about the caliber. BF4 has a Semi-auto Sniper rifle. the SR-338. One shot head shots. Does anyone use it? Me, and that is about it. Bolt actions are not obsolete, only poorly chosen bolt actions would be obsolete. BTW. When you put the DLC/Straight pull bolts on sniper rifles in BF games.... It essentially makes it a low ROF Semi-Auto in function.
As a Marine who served as a Designated Marksman, the there is no discernible difference between sniper rifles and designated marksman rifles of full caliber nature. If they wanted to have designated marksman rifles they should have put an M38 in there vs an M39. That was originally used as a sniper rifle anyway. The only reason why DM's use Semi/Full Auto weapons is because of moving with the Fireteam/Squad. A bolt gun only makes you .0999% more stealthy than a semi gun as a sniper because you don't have an action cycling unless you need it to, therefore not ejecting brass when you don't want it to.