Personally I'm more than happy to give GDL 95% of the credit for taking the little they gave him and managing to make enough of it to make a deep connection with the audience. 5% to the writing since they didn't really do that much with him and even that RTD only gets a small fraction of the credit for since he only wrote two episodes of Torchwood in the three seasons. I will give him credit, though, for letting his little friend, as you pointed out, do most of the thinking in this case and keeping GLD on because that, I think, is one of the smarter decisions the show ever made.