People want solo lane/Jungle Leona, but

Heres why it wont work without significant buffs. She has no shield/sustain to keep her in lane vs other sustain/shield champs. She has no poke, or realistic way to punish for CSing. She has low burst damage. She cannot farm from behind. She can not build into MR effectively.(In this mage heavy meta).

If Leona is to be a solo laner, or jungler, a few things need to be addressed. Her lack of clear. her lack of longevity. her passive needs to be changed to not make her a problem in the bottom lane with buffs to the rest of her kit. her damage needs to be buffed back to Season7. so...

Remove Sunlight-Replace with Sunfire- Essentially turn her passive into a level scaling sunfire cape that activates during her W and her W's residual effect, and remains until Eclipse fully dissipates. Q- from 10/35/60/85/110 to 35/65/95/125/155. Additionally attach a barrier effect to it(Leona gains a barrier for 5% of her current health at all ranks). Increase the CD by 1second across all ranks. W- Leave it exactly the same. No CD reactivation/deactivation on the Sunfire effect. E- Add a barrier onto it(If it connects) barrier scaled based on amount of enemies within a certain radius and based on health(Think Jarvans W). R- Keep it the same, but Instead of adding damage onto her autoattacks/applying sunlight give her a temporary buff that 2x/2.5x/3x's the duration of Eclipses residual effect

She now has wave clear through sunfire on her W/Passive. She now has lane longevity through access to barriers, and would take sustain runes.(Like Poppy) She isn't dependent on teammates to function. Her bot lane effectiveness wouldn't really change. Offensively shed be the same since she lost Sunlight. Defensively shed be stronger, and probably closer to on par with Alistar.