Oooh. I really like this item. Too bad it's not good enough to get often. I usually get it if I'm ahead and we just need a little more damage and I know we're going to win anyways even if I don't have a better tanky item. So I only end up getting it rarely. I mainly like it and get it for its passive. That's what I'd say its most important identity is for me. Giving team extra damage and even some lifesteal. Well, mostly the damage part, cause like, I don't know if Vampiric Scepter building into it is suitable for it. Cause you get Vamp Scepter, yet when you get the full item, the aura gives your allies lifesteal and not you.
So you maybe you could tweak it to give allies extra AD/AP and get rid of the lifesteal part on it. Cause I really don't think that Vamp Scepter should build into it, especially since you don't get any of the lifesteal yourself from Zeke's. I think it's better if you have top Renekton, mid Zed, jungle Warwick. Cause it gives no AP bonus and would be wasted on AP team comps.
Maybe give it something like 30+ AD (to make it better, like a buff, and to make up for the loss of lifesteal), and however much AP. Maybe 30AD/50AP, or....you could have it give something like 10% AD/AP kind of like what you did with Dragon.
The 20% CDR is nice, but it's wasted on champs who get something like Iceborn, Locket, and Crucible or something. 2 of those is nice, but I think it goes over 40% CDR with Zeke's if you have 2 or more of those. Sometimes I'll get Face of Mountain, Locket, and Crucible. Which is 30%, so the 20% CDR would be wasted if I got Zeke's with those items. Maybe give it 5% or 10% CDR, and give it other better stats in exchange. I'd say it's extra damage aura fits its identity more than all that cooldown does. Oh, I have an idea. You could make it similar to Locket. A bit like this.
500 health
50 armor
5% CDR, or 10, I guess
Passive: Flat/Percent bonus AD/AP to allies.
Maybe an active as well. Cause I feel if the extra damage actually helps your team win fights better, then you should get assists off it somehow. Cause I think it can be really good for that.
Edit: PS, if nothing else, at least take the Vamp Scepter out of its build. That is the most awkward thing ever. What if the support chose to get Vamp Scepter first. "Why does Leona have a Vamp Scepter????", "Uhhh.....for the only support item that builds out of it". So I'd say that most supports get Kindlegem first, then wait till they can upgrade it fully. Cause that's what I do. Would you walk around with a Vamp Scepter until you get 1650G to upgrade it?? As a support of all roles.