In mumāthalah, one or more corresponding words across the clauses are aligned by pattern; the concise definition of muwāzanah concentrates on balancing the terminal expressions.
Analytical illustration: Imagine two clauses containing more than one corresponding pair in similar morphological patterns but without a common rhyme. The effect is broader than mere equality between their final words.
The lesson is that rhyme and metrical or morphological form are separate dimensions. Neither should be inferred automatically from the other.