So borrowed power systems you put large amount of time into and they apply nowhere else in the game except in the specific content designed for it that is never added to ever again and is retired. Like Blizzard will never add more levels to the heart of Azeroth or more Azerite gear.
They will never add more Class Hall quest to expand your legion Artifact. It is a not a core system system or support but a parasitic mechanic solely designed to leech time and investment for no actual character progression.