The problem is the shield being in the game in the first place. It was pointless in Modern Warfare 2. It was pointless in Modern Warfare 3. It's still pointless now.
I beg to differ. You can hold down capture points quite well if you have a cooperative team.
For example, in turbine B flag, most people will camp at one end of the fallen turbine, you can position yourself so that your just ahead enough to cap the point and not be open to the flank to the sides. And most people will try to kill you before they go for your team so that helps when several people move to capture a point. Slap on concussion and tomahawks with fast hands and you can defend yourself while they throw their Betties at you.
That is, until the hunter killers, semtexes, and rcxd's come out.
Beg all you want, that won't change how useless the shield is. In the instance you described, I would lob a grenade over the shield onto the flag. Boom, double or triple kill. If that idiot with the shield wasn't there, I wouldn't have gotten a free toss onto the flag because the people on the flag would have been able to shoot me.