Most of the complaints about Vladimir come from mid laners which play mages
And this makes sense since when playing against an AP champion Vlad can just rush a
then become virtually unkillable, both due to the magic resistance and due to the increased sustain. From there he can build full AP. If for some reason Spirit Visage is not enough to deal with the enemy APs, Vlad can also opt to rush
(or he can even use it in lieu of Spirit Visage for more damage, but this latter is usually considered better as a single magic resistance item for Vlad due to the increased sustain)
It is important to note that Vlad didn't purchased Spirit Visage before because not only he was not allowed to do that due to Will of the Ancients being a mandatory purchase, but also because WotA itself offered enough sustain for Vlad and he didn't needed to use Spirit Visage. Now he does that not only because of the lack of WotA, but also because Vlad's sustain by itself isn't actually that amazing, he needs Spirit Visage for it to be relevant.
Also, APs do not have a good options to itemize against Vlad, for example, Grievous Wounds: They have
, but good luck even getting Vlad below 35% health, especially since with Spirit Visage he becomes incredibly resilient to magic damage. Morellonomicon is also bad for manaless APs due to the mana and passive mana restore on kills being completely wasted. Also, APs do not have a consistent magic resistance option which works for everyone. The closest thing is
but this item is not attractive for mages which have too long range on their spells due to the aura range being limited. There is also
but this item does not offer any AP.
Compare to AD champions.
Vlad's currently only good option for armor is
and this item does not offer that much armor. Other armor options are not nearly as good for Vlad, for various reasons (Thornmail actually used to be viable back before they nerfed the passive)
Also, AD champions have a very good consistent GW option:
. Not only this item activate at any level of health, but all you have to do is deal any sort of physical damage (auto-attacks or spells) and GW is already affecting him.
They also have very good magic resistance options which work for every single AD champion with no downsides:
on top of that, ADs also have lifesteal if they want sustain themselves, while APs have no spellvamp options ever since WotA has been removed (and even when WotA existed, it was good only for very few APs)
TL;DR: Vladimir works very well against APs and is not very good against ADs, and that's due to itemization. I don't know exactly how they could solve this without directly nerfing Vlad, but I think that buffing Morellonomicon is a good start. I don't even know why they nerfed it to begin with.
into vlad and just never lets him near him.