...why would you ever not run copper alongside fiber for new construction? If nothing else, PoE is extremely useful, and nothing says that you actually have to connect all of that copper cable to your switch... you can connect it as-needed. I also can't imagine that most refits only have room for exactly one cable in their conduit. [0]

I'd expect to hear the sort of plan you propose from a PHB or Highly Paid Consultant, not someone who actually has had to use that sort of configuration.

Regardless, the scenario you're now proposing is one where noone other than a PHB would use that Amazon Special that you linked for media conversion.

[0] If there's no conduit and cables are all flopping around in the wall, then there's even more room for cabling.