First , if everything Kamiya says is true, so Bayonetta ( only a witch) can easily beat Dante and wip the floor with him.
Second, the classic image we have from Eva is that she was fully and simply woman, with a strong soul, but a weak body and that's the beauty of the story: a powerful Demon falls in love with a normal woman and marries her. She was so normal she dies trying tro hide his little boys, not in a badass fighting.
Sparda turned his back to his race and came to human world to live like a human, because he wanted too, not because of a love interest.
Now, Eva being a witch in Kamiya's terms:
Eva, a truly extraordinary witch entered a contract with a legendary dark knight and then faced( herself) the amassed armies of Inferno" Now our Eva is not only a "guile heroine" but " army of only one woman".This insinuation is absurd.
Why I have problems with Eva "selling" her soul: Sparda becomes a human, so it would be logical if he married her was on human ways, not taking her soul( whatever it could means) to him, like the other demons usually do.Now if Eva was a witch similar to Kat( who never lose her soul and have human weaknesses I could swallow), but what Kamiya is implying is absurd.
From her part, giving her soul, even if for love, is not different from giving her soul for whatever mundane reason, like any other human would do.It was no better than Vergil wanting power and do whatever it takes to get it.
Kamiya does this act of despise towards the fact of Capcom continued DMC without him. He, with his intromissions, is corrupting whatever DMC canon says, because he is full of himself, making almost impossible to Capcom continue DMC original canon, since he knows whatever he says , people are willing to follow.He even says Lady and Nero doesn't exist when asked by fans.
Sorry for the long post...