Here is a gross misunderstanding of melopeia, by a stupidly incompetent literary critic. I can think of many definitions of melos in poetry.
1. It could just be a function of poetry actually set to music, having a historic connection with a tradition of vocal music. That's melopeia(1).
2. Secondly, it could be a kind of mellifluous quality. Smooth sounding verse, like Spenser "Sweet Thames." Melopeia(2).
3. Next, it could be applied to metrical and rhythmic skill generally, whether or not this skill is directed toward smoothness. After all, you can have skillfully rough or shaggy effects too. Melopeia(3).
4. It could be a function of how prominent or salient sound is in the poem, in relation to other elements. Melopeia(4).
That's just getting started. I'm sure there are more. You notice I never mentioned metrical regularity as a form of melos. That may or may not accompany melopeia, depending.