Yes. Recall how much metal was in Gresit? Consider how much all of that weighed, in the end. Now multiply it. The weight and stress created for movement, both physical and magical, precludes any kind of organic material. On this small of a scale, it's fine, but to scale up, well. Things fall apart.

[He stands there with his arms folded, considering the prototype for just a moment more. Alucard's arm is heavy with papers now, everything pressed to his side.]

This is all testing the theory, after all. Changes in design were bound to happen.