An idea for if Leona's passive ever needed a change/buff
I doubt Riot would do this one right now, but say they wanted to give Leona a little more utility, they could try this upgrade to Sunlight.
If Sunlight is triggered on an enemy Champion, the ally who triggered it gains a 2-second shield.
This would give Leona more ability to "protect" teammates, without giving her a heal.
Just a thought for the future. She doesn't need buffs right now, but if at some point she does, this would be a nice add-on to her.