I'd put Luther in the same boat as Mary J. Blige.

They're demi-gods among mainstream black listeners yet only an occasional presence with the white masses. General white listeners know them, sure, but aside from an occasional crossover hit (Power of Love for LV in the early '90s; Family Affair or Be Without You for MJB in the early to mid '00s), they're not on their radar like that.

But they still know who they are.

Now, Frankie Beverly & Maze, on the other hand. VERY FEW whites will know who they are even though they're legends for many Black Americans of various generations.