PLEASE READ THROUGH BEFORE GETTING "TRIGGERED" AND POSTING! This isn't about her being WEAK right now.
I found changes for Leona that I feel would keep her 100% viable and primary as a support(even though she is listed as Tank - Support like Naut, Alistar and Blitz who can all jungle/lane) But will give her not only solo power in other lanes, but make her less helpless when building off meta or is caught alone. All without making her more overpowered by making some compensating nerfs.
Sunlight: can now be procced by Leona's basic attacks(ONLY BASIC ATTACKS!). This change gives her some dueling power, but her potential burst will be nerfed on some other abilities to compensate. To help compensate Sunlight's damage is nerfed to 15-100 from 20-105.
Shield of Daybreak: Unchanged.
Eclipse: Damage reduced to 30/77.5/125/172.5/220 from 60/100/140/180/220 to reduce early burst to compensate being able to proc her own sunlight. Late game damage remains the same.
Zenith Blade: Cooldown is now 16/14/12/10/8 from 13/12/11/10/9 This change reduces her number of early game dives with her extremely easy engage tool, to compensate her bonuses elsewhere.
Solar Flare: Damage reduced to 100/150/200 from 100/175/250 Reducing her late game damage to compensate for her Eclipse remaining the same at rank 3. Meaning late game she has to get INTO a fight to do full AoE damage.
Enhanced Basic Attacks: 3/4/5 Unchanged
Bonus Magic Damage: 20/30/40 (+ 15% AP) from 30/40/50 (+ 15% AP)
What do these changes do? These changes are subtle but effective. In supporting it nerfs her a tiny bit, as she is very strong and has a high win rate right now. As proccing her own sunlight is not as important early game in a duo lane where it would be procced by the ADC and ganking Jungler. Unless she procs her own sunlight when it would normally be wasted by another application, then it is a slight buff to her damage output and the only nerf is to her early game AoE and her early Zenith CD making her easy engage a bit more reserved. At the same time, Zenith is rewarded with a shorter CD late game, and Eclipse does the same damage late game, so she is straight up buffed late game due to being able to proc her own sunlight. EXCEPT that her ult, to compensate, does slightly less damage on lvls 2 and 3.
It makes Leona a beautiful warrior, she would have more combat power when alone, and being able to proc her own sunlight means even with early nerfs to her W damage and late nerfs to her R damage she still does slightly more dmg in extended fights. So not only will she become less helpless as a support when alone, but also could take up solo lanes such as top or maybe even jungle.
Why do I care? I love Leona, as a support. But recently with all the armor pen and burst and dps in the game, by mid-late game I can be 2500HP and die to a 350HP Ashe who just lifesteals and DPS me without me being able to respond due to ineffective damage output of my own. I don't want to beat carries straight up, that isn't my job. But if a low HP squishy comes after me, a big shield wielding, sword swinging warrior should not be helpless because her passive does absolutely nothing for herself.
If you like the general idea but find it too strong or too weak. Please upvote and leave a comment suggesting how you would go about the changes.
EDIT: After comments from Lord Desert, I have come to the conclusion that a possible 'fix' that doesn't change any numbers or gameplay is this.
If Leona reapplies Sunlight on the enemy 3 times without an ally proccing it, it goes into "Solar Meltdown". This causes it to reduce the enemy's Armor and Magic Resist. This makes Leona able to fight enemies alone without an ally, and solo lane. Without changing how she supports at all. It would still be ideal to have your ADC proc sunlight, but if you are alone and hit them with EWQ or REQ or whatever else to get three stacks. You still get a personal bonus that would make combat against them possible.