Here's how I'd buff turrets

tl;dr double shots

First of, I can see why you wouldn't need to. They're doing their intended job. They protect early and need to be protected later on. If the enemy team gets aced, they misplayed, no two ways about it, misplays deserve punishment.

But it's honestly a little silly how you can draw aggro and proceed to herd your paltry minion wave towards the inhib. Turrets should be some level of imposing in some way. They're big, glowy structures that shoot spheres of light, after all. Their resistances are high enough when no minions are nearby. Imposing. In terms of damage, they are too, they halfhealth squishies with 2-3 shots mid-late, that can be taken advantage of, so it's imposing I M O.
Being so easily deceived, on the other hand, doesn't quite get that image across. So in detail, here's what I propose:

When there are no allied champions nearby, when a turret targets an enemy champion, it will halve its damage to target minions in addition to that champion.

That way, the turrets won't shoot themselves in the foot by tickling the enemy tank instead of doing something about the nearby minions cutting their defenses down.