Diana also can't reliably jump on the enemy Pre-6 to proc her passive and has to rely on her basic attacks for it, unlike Ekko who can just land both hits of his Q and then E on to the enemy, or just E on the enemy, throw out a point blank Q and then auto attack.
Also with Diana, if she uses her ult on you to get on you and proc her passive, she's basically there stuck fighting you (or if lucky enough, could dash to a minion to get out). Unlike Ekko who can jump on you and then proc his passive and with the insane Slow + movement speed on it, can easily just run out of any danger. Not to mention Ekko's insanely strong utility AND Damage on his Ultimate...Even if he doesn't use his ult for damage, the utility and safety of it is op.
Also Ekko's other skills are technically stronger then Diana's to. Ekko's Q is stronger then Diana's (if he lands both hits), sure Diana's shield skill deals more damage than Ekko's E on normal amount of damage but Ekko's E also applies on-hit, spell effects and has a lower cd when maxed. Ekko's shield is much stronger than Diana's and Ekko has a 2.25 second stun which is much stronger then Diana's small knock-up into slow. On top of Diana having more mana cost than Ekko.
So sure, on the damage side...Diana's passive is barely stronger then Ekko's is but Ekko already has so much things on him that is way better then her that his passive (or something) could really used being toned down.
