While I'm not part of the debate, I wanted to point out that lack of efficiency isn't a strong argument against design itself. It's a strong argument against continued design. If I made a hammer, and was satisfied with its design, I would keep making hammers the same way I'd been making them, even if it wasn't as efficient as possible. Where efficiency generally comes into play is when you have competition. In that case, in order to do well, you need to improve the design of your own hammer and/or give it capabilities that a competitor's hammer doesn't have.
Efficiency doesn't sufficiently argue against the idea of an initial design, way back when. But it is more than sufficient to argue against the idea of continued design. If you're satisfied with the way you made something, why would you upset your own applecart in making changes when it costs you extra time and money to make something that might not be as satisfactory?
In short, Godexists might be able to argue that lack of efficiency is no bar to God making initial designs, but he can't argue against it causing a problem for continued designs, especially if those continued designs incorporated improvements from the originals.
Of course, this all begs the question of how we know there was a designer in the first place, which Godexists has never sufficiently answered. Logic doesn't cut it because you can prove anything with logic, even something that clearly won't work in reality. That really needs to be the first question he answers - where the evidence for this designer of his is. If he doesn't have evidence, there is no reason to conclude that there must have been a designer.