While this one agrees on almost all points (would allow more base stat variance based on affiliation perhaps but that’s a long side bar), especially the loathing for the hidden modifiers and fluctuating multipliers, finding Tier 4 Fighters for the lowest of factions is easy. Exiles have at least three guaranteed named thrall spawn locations, Cannibals have the Ritualist and Thugra as fixed spawns and there are three places where Cannibal Brutes are very common even if not guaranteed. Likewise Pirates have Sully and Tarman, as well as several places that can be Hekkr or Gall o Spear. Then there are the at least three locations with a wandering Tier 4 in the Jungle.
Lemurians are the faction that seems to have the least chance of finding a named character, and even then, they are far less useful than their stats would indicate.
One thing that you mentioned that is especially excellent is the idea of named thralls having their own specific perks from leveling. Much like the playful pups in Siptah. This would be a great way to make them distinct from the nameless Tier 4s.
We have generic tier 4s for several factions.
Berzerkers for Cimmerians (and an unimplemented Berzerkers for the Nords).
Treasure Seekers for the Relic Hunters.
Claws of Jhebbal Sag for the Dogs.
Captains for the Pirates (altho they seem to only have a single spawn point).
Brutes for the Cannibals.
Also, in addition to making them distinct from the nameless ones, it could make them distinct from each other. Suddenly Lian and Janos have a difference other than male pattern baldness.
TLDR; Very premium idea.