>>20107895indeed, and gf isn't really the most consistent with that.
you have nido-tier, which have different stat totals and movesets.
you have meowstic-tier, which are of the same species in the pokedex's eyes, but get different level-up moves.
you have unfezant-tier, which are simply visual and nothing more
and you have everything else, which have little to no difference between the two.
but if they're not the same species, how can you breed one and get the other one, even if that pokemon wasn't involved in the breeding process ?
[eg, you can breed an illumise with a ditto and still have a chance to get a volbeat]
also, since when was unfezant a peacock? they don't look alike, the male even less so.