The maps are designed so that the medium can just about go everywhere the light can, and when everyone goes to the same locations, the light's squishy-ness really feels bad.
I'd rather they nerf the amount of pips they have, and the regen rate, than gimp the lights survivability.
The restriction on weapons feels like it makes up for the light's mobility, that and restricting how many abilities they can use would probably balance them just as well as gimping their survivability.
To utilize the wjing aspect the light has to put himself into an open environment, with restricted aiming ability, while heading towards the
(after all the guy furthest in front is going to die more, if they're already weak hp wise, they're going to get wrecked)