Leona is perfect for jungling; amazing ganks, OK clears, good against the assassin meta, synergies with devourer amazingly, doesn't really fall off late game, can build tank if behind; She brings amazing amounts of CC, damage, and peel for her team, with a good pick potential.

Dev is super Op right now in general, and Leona is extremely good with AS, her aa>Q>aa combo will burst *****es down in no time. Cinderhulk sounds ok, but honestly you are better off with devourer into sunfire if you need tank stats. She has no AD scaling so warrior is kind of a waste, and Runic echoes is decent if you build Ice-born Gauntlet and more tankiness after it.

Your E is such a good gap closer you can literally run into a warded lane, flash E>Q and get a kill. If you have ult you won't even need the flash.