Putting Enuo in the game isn't necessarily a bad idea, but the way it was executed in the GBA port was terribly lazy. They were clearly just looking for anything to use as an extra super-boss, just like how they based an alternate form of the Emperor on a slightly different-looking piece of concept art for FFII, and ripped the Easy Type sprite of Zeromus for the inexplicable "Zeromus EG" for FFIV.
Except, once you've beaten him, you have nothing to use the Necromancer job on.