"April is the cruellest month, breeding Lilacs out of the dead land, mixing Memory and desire, stirring Dull roots with spring rain. ..."
"Oh, when I was young and easy In the mercy of his means Time held me green and dying, Though I sang in my chains like the sea."
"Things fall apart; the centre cannot hold; Mere anarchy is loosed upon the world, The blood-dimmed tide is loosed, and everywhere The ceremony of innocence is drowned; The best lack all conviction, while the worst Are full of passionate intensity..."
Those don't rhyme either, but they're poetry right enough.
For poets and songsmiths rhyme is a resource, not an obligation. If the poem/song works for its intended audience, then whether it rhymes or not matters little. Despite the missing rhyme in verse one, the MacPeake version of WMT has lifted the hearts and voices of audiences for many years, and long may it continue to do so.
Other versions or variants also have their devotees, and good luck to them. Scholars may debate which version of text or tune is the 'original' one, if they wish, but no Central Committee of the Folk Party has the power to decide which is the 'correct' version for singing.