Which are ... the same thing ?
NO, among the each meito grade each blade is ranked from strongest to weakest.
Yoru is the strongest meito in the world because it was made a black blade, Mihawk and Tashigi have confirmed this that kokuto yoru is the strongest blade in the world.
Hitetsu also said this pretty clearly that if Zoro manages to make Enma a black blade that it would increase in "rank" meaning among the 21 great grade blades it would probably rank first among those blades.
Never was it ever stated that Enma will magically change its grade from great grade to supreme grade.