There’s probably a little more that goes into the rating system than just the hair, like costume complexity, number of sculpts, or the quality of materials used.
They’ve also yet to announce anything that’s fully sculpted, such as a Cyborg or T-800 type figure so who knows how they would factor in. Presumably, that’s much simpler than working with a multitude of microfibre materials to tailor a perfect, to-scale outfit.
Superman could either be the standard Hg rating due to no rooted hair and a single fabric suit, but we are getting two capes, two sculpts, plus a chrome body, which could easily bump it up to the Advanced Ag level.
Something like a Nazgul is a clear Hg due to no sculpt or a particularly specific form that needs to be replicated perfectly to scale- such as Cavill’s physique.
We’ll figure it out in a few years after InArt have actually released a variety of figures.