A large portion of the community will always flock to whatever is easiest to use. Nerfing the Harrier significantly enough to remove it from that position will only see it replaced by another. If your only desire in a Harrier nerf is to see a more diverse set of classes and weapons used, I suggest you give up hope.
I see a lot of TGIs and ALL of them carry a harrier 1-3... then I break out my harrier 10, sit for a while then change back. BWAHAHAHAHA. I don't mind people using the harrier (plus the majority of TGI score comes from spamming overload, you could probably outscore one easily by using the Geth Engineer and spamming OL + Turret, hell I regularly outscore them with my Human Adept even if it's following me around)
TGIs only annoy me if I'm playing as a Biotic or using a class with grenades (it bothers me when the TGI sits out in the open, spams all his stimpacks then takes all the grenades from the ammo boxes)
I like to use my lvl 1 TGI/Harrier after I promote my Infiltrators and don't feel like playing a silver match to lvl up.
GT - Xero M XTC http://social.bioware.com/n7hq/home/inventory/?name=Xero%20M%20XTC&platform=xbox
Take away the Harrier, and all you'll see is Particle Rifles. Take away the Particle Rifle, and all you'll see is Typhoons. The best weapons will always have more people using them, nothing will change that.