I think reduced mobility is a good counterbalance for shielders. I honestly do not want every schmuck with a 100+ speed sabre/pick facehugging my 7-8 Athletic 2hander/polearm builds cuz then why the fuck do I have agility instead of strength in the first place. As a shielder the only classes I can't facehug are lightly armored agility heavy builds which is intelligent internal melee balance.
I just think it is so easy to be aggressive as a shielder already, to close ground, and fight on the front line that a moblity buff for the general masses is not needed. If you want to be fast as other classes, don't take a shield! I always used Elite Cav shield just because it is light. If you want shielders to pick apart ranged more, then try rebalancing how sprinting and kiting works for ranged (based on weapons in their hands disabling or nerfing sprint or something) instead of screwing up melee balance.