I'm on the same page of you. 300K mastery, gold onetricked her, 5.5KDA- in norms- and today I fed.
2 hours; dedicated to learning and setting up the runes, only aftershock immediately grabbed me as 'for leona', the scaling tank ones are a wide miss for support tanks. I wasn't happy to see some of aftershock's powerbudget put into damage -that means it's not in tank stats. 'Leona is a tank, I'm sure the other runes are just as bad for other classes' I say to myself, trying to rationalize the failure.........
.... I witness firsthand how out of control damage is- facing Jhin (a poke adc, usually no problem for Leona) I lose lane slightly- I try to play macro when my adc is safe so we can get ahead, only to realize my EXP isn't going up (too late! Now I'm behind!). Pointlessly try and save my carries from burst with locket + gargoyle before realizing there's just too much burst, and then my team flat out tells me- with that build, I'm just not a tank, because I had little over 1500 HP- Yes I had some armor, but that's pitiful. I blamed the runes, 'I picked the wrong ones... that's all, right?' and tried a variation much closer to, but not yet, optimal- More failure, my biggest problem being even playing safer, I just can't save people. Then I tried Thresh, and watched my adc disappear before I could throw a hook... Tanking nerfed, Macro nerfed, Peel nerfed. I've been pretty furious all day.
Now people are crowing about how damage is great on Leona, because fervor was played at Worlds. Yeah, I saw it. I'd already been there, done that, happy to see it in Worlds, and I understood why it worked, and when it won't work. You can't just copy ONE LCS strat and throw a fervor style Leona at everything. But y'know, most people never saw the value of a tank in the first place, they just think we shove CC down people's throats and then yell 'stop getting Blitz hooked!' at us after we've bodyblocked it 6 times in a row. They don't realise, if you're poked out of the frontline, they're dead. Perhaps right now, it's true and doesn't make any difference. But I find this game, in its more well balanced states, isn't just 5 v 5 burst assassins (even if one of those assassins is Leona.)
To help I'll share my updated runes- I've not tested them out, maybe they can be improved, so goodluck. Resolve > aftershock, font of life, iron skin, second wind, Domination > taste of blood, zombieward. Taste of blood procs Iron Skin (or the MR alternative) - Second Wind protects a little from the poke but that's all she wrote. I'm waiting on an I0ki stream to see what he's doing. Until then,