Here Riot, I'll give you a free example of a resolve rune that people would actually take.

Fortitude of the Titans: When below 10%-40% health (scaling with level) take and deal % reduced damage equal to your % missing health.

Lv1 10% Lv6 15% Lv10 20% Lv13 30% Lv16 40%

In addition to the damage reduction, grow in size when active.

(60 second cooldown when out of combat for 6 seconds.)

That way the people who want to get tanky can get tanky and do less damage.

I'm surprised there are so few things like this.