Bike porn

No, to be porn it must have both. Assuming, for the sake of argument, that the Mercian needs a zero offset post, the Easton EC90Zero is objectively better (by some measures, at least) than a Thomson, but it would be an even worse aesthetic choice. If you concede that there is a post which is objectively better than the Thomson, your proposition is that including such a post in this build, regardless of aesthetic considerations, would make it more porn.

The Mercian has already prioritised aesthetics over function by being made from steel and having a quill stem, so a small increase in weight to accommodate a more aesthetically pleasing choice of seat post which does the job just as well as the Thomson would be entirely in keeping with the ethos of the build. In my opinion.

fixed.