I don’t think Toby needs to be played as slightly off. It’s enough that he come across as traumatized and subservient, as if he expects the crap to be beaten out of him at the slightest mistake. And if the role is played by a child or teenager — or someone who comes
across as one — I think the oddness is even less necessary. The “not quite right in the head” take probably works best if played by a clearly adult actor as an indication that the lifelong abuse in the hands of Pirelli has led to Toby’s stunted mental development.