Riot you done goofed
Nerfing Ekko by 4 AD doesn't nerf tank ekko. It doesn't nerf him at all.
Nerfing Vayne by 3 AD is more significant than that nerf. More AAs = more it effects them. You basically went up and went "Man Brand is overperforming as a burst mage" and nerfed his AS.
How to nerf tank ekko.
Passive 20-190->20-150 damage base.
Q: Slow 32/39/46/53/60 -> 32+(~.1 AP)%.
Ult: 150/300/450 (150% AP) ->125/225/325 + (175% AP)
Is it really that hard. I mean seriously. Take away his base values and give him scaling. It isn't hard. Not is it rocket science. These changes will literally kill tank/bruiser ekko for good as he is not healthy at all.
less effective on him. The spellblade effect works off of base AD