Fuji Track / Fuji Track Pro / Fuji Track Classic

What's an audaxs?

My point, is that they spend 12 hours in the saddle. Comfort is the most important factor. If 23c was particularly uncomfortable, then they couldn't use them.

Comfort is more down to saddle/shorts (ignoring position) than anything else. imo.

They also want to ride at a good pace for 300km. A 500gram tyre might not be the best choice for that.
Also a bit of an assumption that all 28s are more comfortable than 23s. A stiff walled 28 like an Armadillo will probably be less comfortable than a supple 23 like a GP4000 IMO.
I would guess the Rando is in the stiff wall category?