Yes, it is really unfortunate that superior and mastercraft are available so late in game.
There are various mods that swap armor textures. As an example, if you're on PC I'm pretty sure you could swap the Kaer Morhen texture with the texture of whatever armor you want but it won't keep it's stats. If you swapped the Kaer Morhen texture with anything, it would retain the Kaer Morhen stats but obviously have a different appearance.
IMO mostly the point of getting Ursine Armor is for the Adrenaline Point generation. It looks nice but if you're gonna run a combat build, that armor is mostly the way to go IMO, especially if you're building on Adrenaline Point skills.
It is indeed extremely frustrating to have to level to the correct level to even get the Ursine Armor set if you're leveling up in the combat tree.
I agree, it is so frustrating to only be able to use the mastercraft gear for the very end game. And since we are at it, please make Kaer Morhen available at any level, so the Wolf Set base set is at least accessible before finishing Velen and Skellige.