Does Leona need anything to improve her? If so, what?
Leona's great as an initiator, has some of the best CC around, and is really tough to kill, but these things only happen if she gets ahead. She unfortunately has a low pick rate in high tier play because if she gets behind early, she stays behind and generally cannot recover. She's also easily counter-picked by Janna, Morgana, Alistar, etc.
Meanwhile, super-supports like Thresh, Braum and Zilean out-strip her usefulness because even if they fall far behind, their base mechanics mean they will ALWAYS have a role later on. Zilean can always Chronoshift a carry, Braum can always inflict strong stuns and block shots, and Thresh... don't even get me started on him.
I feel like this started the moment she got that "love tap" nerf a few months ago, where she lost base health regen and -5 AR/MR on Eclipse. Granted, Riot will not revert this without good reason, but it still sucked to see my Solari get nerfed, which put her into less-than-ideal territory. It could just be a kind of power-creep for the supports, but I feel it goes beyond that.
I doubt too many people agree with me on this, but I think Leona might in the future need to get her kit upgraded. It works very well at its job, but said job tends to be unwanted or found better on said super-supports.
IMO, this is what I think should be done for Leona.
P - Sunlight: If an ally triggers Sunlight on an enemy Champion, they are given a 2-second shield. Shield strength is equal to Sunlight's damage. Shields do not stack, but refresh if reapplied.
W - Eclipse: Same AR/MR bonus as before. While active, nearby allied Champions (within 400 range; does not include Leona herself) take X% reduced damage from all non-tower sources. This damage is instead dealt to Leona; damage type dealt to Leona is the same as the original source, and is reduced by appropriate resistance. Leona cannot transfer damage to herself if she is below 5% health. Does not work against true damage.
These might help Leona a bit in her support-tank role. The W change would be particularly good, as right now any smart enemy will almost never target Leona first, even if she's isolated from her teammates.