Issues with the shield towers.

I've got a couple problems with the towers that give shields to champions. I understand that the point of them is to stop poke and siege comps, and for that, they work pretty well.

But they also deter chasing, towerdiving, global ults, and every way of finishing off an enemy before they retreat too far for you to follow. It's a bit ridiculous to put so much work into trying to kill someone only to have them gain a 300 health shield and get away. Also pretty dumb to try to finish off a low health enemy with a Requiem or Trueshot Barrage only to have them retreat back to their turret and gain a 300 health shield. Ya hear me?