A lot of the very few surviving samples do of course look really primitive, but at the high end, cobblers in the Roman world were not fuckin' around.
UC28327 here is a pretty ornate sole with a very modern shape.
The upper on this one must have been super nice when new.
Then, there's no reason to suppose that Marcus Aurelius' (and/or Hadrian's) sandals on their statues were idealized past the point of plausibility, though I'm sure once one government contracted statue with approved Imperial sandals gets made, there's a temptation to stick with the motif regardless of the current Emperor's footwear preferences.