We can find players useful when they are either good at IS, or good at both JS/IS, but without IS? Sorry, 3-2 zone will definitely take good care of you.
But then again, if we make JR cheaper, we start banging our heads at a new wall - completely overpowered players with waaaay too big tsp's. A.k.a power creep.
Because there will come a time where a 20js/20jr/20is wont even be much of a big deal without salary restrictions.