You are approaching this completely the wrong way. They're mages and demons, while you are seeing this like they are regular people where on one of the two a neurosurgeon locked of some senses. That logic is misplaced.
Evergreen could turn people to stone by looking them into the eyes, still it didn't work when Erza only used her artificial eye. Why? Why would it matter that her eye is artificial? It does the exact same thing as her regular eye and should be connected more or less the same way as her original eye was with her brain. In the end the components of her original eye got replaced with other components that do the exact same thing. Logically speaking whether she has an artificial eye or not, it shouldn't matter, she should have been turned to stone by Evergreen. But she didn't. Why? Because her eye is artificial. It's 'different'. That's the logic you apply to FT. Hence Erza having an artificial eye is enough a reason to justify her being able to do what she did.
All your neurological stuff can be discarded as you are applying it into a context it does not belong. Kyouka uses a curse, she is not a neurosurgeon. You are acting like curses and magic, things that do not exist in the real world, somehow are just names for things that can easily be explained by real life science. They can't, at least not fully. You are assuming that her curse by default causes a physical change in her opponents, while it easily can have no direct physical change at all. It could potentially take way someone senses without changing anything physically. Why? Because it's a curse and it's Fairy Tail. That's the kind of logic you have to apply.
I realise whilst these are mages but at the end of the day all are humans not ethereal spirits and are bound by the laws of biology, a person is killed by Elfman's magic not because of certain magical element but due to his increased strength he causes blunt force trauma or any other traumatic injury to the body, Grey will surely use his ice magic to defeat an individual but his ice magic effects that individuals body i.e his ice magic might cause plethora of biological effects from hypothermia, frost bite to trauma.
Kyouka uses her Sensation Curse, which heightened Erza's response to pain due to torture and also rendered her 5 main senses useless, these two things in real life are contradictory as without her sense of "touch" she wouldn't feel the pain and this is possible only if Kyouka was effecting her mind not her body.
She chose to pause any external Stimuli, which Erza could use in battle but allowed her brain to perceive pain, this can only happen if her curse works on Erza's mind i.e. on a neurological level.
Also Erza could overcome it due to her will power i.e. she took control of her brain back, this would have been impossible had Kyouka's curse be of external nature.
Kyouka's curse is different from say the magic Natsu uses as his magical is on the exterior physical level while her is internal.
This theory of mine may be a long shot but it explains why Erza's seemingly "different" eyes failed to work.
In case of Evergreen the word "see" is important, those who can't aren't "affected" by it, hence it is an external Stimulus while Kyoka's curse appears to be internal and condition free which furthermore adds to the reason why Erza's artificial eye didn't work.
She doesn't have to be a neurosurgeon to put such a curse on Erza, this can be done by myriad of conditions, blocking her neural network and allowing only pain to be perceived is one such way, taking partial control of her brain etc etc.
I know it has no importance to Fairy Tail but many type of tumors in brain can cause the conditions or interference in neural conduction network due to a disease.
In the end I might be overthinking and trying to mix too much reality into FT but imho this is my theory and until we get an explanation in the manga, it might be right.
