On the first point i am with you. 3v6 because of quitters is not good. I blame the quitters more than the devs though.
On the second point, no. It may be a dumb class setup, but by your own words, they move slowly towards you crouch walking. You should be able to leave the area and shoot them from a distance (aim at their feet, it is very hard to move with the riot shield and not have it come off of the ground) or run behind them and knife them. That is two options where you wouldn't have to change your loadout or use perks you do not want to use. Of course, there are a ton of perks that will guarantee they don't bother you that you can use as well. Dumb, yes. Should it be nerfed, no.
Peace.