Another stat I would like to see would be "Damage mitigated" This would include buffing ally's resistances, shielding, basically anything that keeps allies from taking damage that isn't like, Wind Wall, body blocking, or healing, though if you really wanted to you could also include self mitigation like Wind Wall, your total defenses, or Braum's Unbreakable. I think it's more representative of how much tanks and shield heavy champions actually contribute, because I've had games as Taric (pre rework) against very AD heavy teams where I take almost full aggro in late game fights and take borderline laughable damage because I just had so many resistances, and in the post game 3 teammates took more damage than me because I simply reduced so much damage instead of actually taking it.
This would also benefit supports like Sona and Janna who aren't healing focused and instead rely on mitigating damage with shields more so than healing actual wounds (though Janna and Sona can both heal decent amounts. Would probably be better for say, Thresh or Blitzcrank who don't have actual heals). And since it wouldn't just be something like "Shields applied to allies" it would only count the damage that the shield would absorb, meaning that timing shields to block heavy instances of damage contributes a lot while just shielding allies at random wouldn't really do anything, this way it would accurately show how much damage you kept yourself and allies from taking since a shield that blocks nothing at all isn't really helping anybody (The exception being Black Shield stopping CC from abilities that deal physical damage, but CC is not damage, I have no idea how to properly credit that one).