The best way imo to fix the sniper AC would have to be to make it more like a real sniper.
And the most efficient way for us to be more productive damage wise, is to make our sniper skills penetrate players that stand between the sniper and the target, that way, we do damage to 2 or 3 players instead. It also makes the sniper playstyle more advanced, and challenging, but face it, noone is choosing sniper because it is easy, so it will make positioning critical for maximum efficiency. Also, to not make it way too OP maybe only half damage to Crossfired players. This is just my opinion tho, and I believe it would make a lot of snipers out there happy, even though it is not a huge buff, just a little extra to spice things up!