An idea about strengthening Nexus Turrets

It's a response to another Master Tier example of how weak Turrets are.

You know, in Paragon hero damage is hella lower, turret/inhibitor/core (core = nexus) damage is high enough to kill a tank in 5-10 seconds MAX and games are still lasting around 30 minutes. Yet here we are defending a Sion that appears almost invulnerable to TWO NEXUS TURRETS. Yes, there is a Soraka healing and shielding him. But the damage each turret shot deals to him is insanely low nonetheless. I think the turrets inside your base, or at the VERY LEAST the Nexus Turrets alone, must be really hard to take down and really powerful damage wise, just like "bunkers" as someone mentioned. It does make sense since they protect your most important structure, does it not?

So here's an idea - make Nexus Turrets take 75% reduced damage from all sources and deal bonus True Damage based on the champion's max HP. Once one Inhibitor is down the turrets are exposed - like now. Once two Inhibitors are down - no True Damage. And once all Inhibitors are destroyed - the turrets are weakened to their current state.