But regardless, does that mean that Mithril is just another fantasy element Bethesda just heartlessly employed in TES IV because it would would appeal to potential new-comers?
No, Bethesda's heartless employment of it dates back to Daggerfall at least. But it is indeed just a generic fantasy element Bethesda uses with no explanation given in the lore for its existence.
At leaset in Daggerfall it was blue plate, instead of the usual silvery chain mesh stuff.
Of course, as blue plate, it ended up looking like a plastic toy instead, but maybe with Oblivion's graphics, it could have still looked metallic even if it was a little blue.
Mythril/Mythral should offset Redguards's skin color nicely AND normal silver is a svcky weapons material, even in TES.
I would hardly call it "svcky", being a level above steel in Oblivion, that makes it fairly good in lower levels, not to mention aside from Daedric, it is the only kind of material that can damage ghosts without enchantments in Oblivion.