Before the patch, killing an empty weapon was as fast as shown up on the video (taking into account supression reduces to 25% dps, therefore 2 PTRS takes roughly the same time).
You can kill EMPTY support weapons as easily with 3 Shrecks or 3 zooks. This rises the point, as i've already said, that probably prioritization of target is set higher to the support weapon rather than the crew.
This ^. Just set PTRS to prioritize crew and re-evaluate after that.