That article is merely making the argument that reproducibility on its own does not improve security. This is clearly true. Anyone can also claim that code-signing does not improve security because "well, you have to trust either this blob of software, or this certificate blob, or this signature, what's the difference?" The difference is when you start to compose these parts into a larger system. Dependable qualities of a system (eg: a specific hash function is one-way, or that specific problems are hard/easy to solve) can be used to create the security properties you want.

I doubt Tavis is saying that builds should not be reproducible; just that it is not going to provide security on it's own in a trivial manner. I'd argue that reproducibility can help create secure systems with properties otherwise unobtainable (or difficult).