Even though there are counter-cases, the normal order is words first, then music, even in vernacular genres. Though the tendency in the vernacular is to not worry so much about the priority, or to think of the music and words as simultaneously arising, or with a smaller temporal gap, the words tend to precede the musical setting of them.
For example, there is not a tradition of poets finding musical melodies and then trying to write words to them.
I guess you could write new verses to an existing song, adding lyrical material. A translation of a song lyric would have to match the melody note for note, syllable by syllables, if it were being sung to the same tune.
It's not that music or words are easier to write. That would depend on who was doing it and what the standard of being a good or bad melody or set of lyrics was. But all other things being equal, it is easier to set a text to music than write words to existing music.
Of course, when I sat it is hard, that is meaningless, because I could easily think of a phrase or two that fits the melody of Ode to Joy:
We have time to finish dinner
Then we'll watch a Netflix show...
Or Jesu Joy of Man's Desiring
We'll have some dinner then shopping and zen meditation we'll live out our lives in a state of perpetual motion and stillness and never will darkness become our condition we'll never say never to all the great life possibilities facing us now
The trick is to get from the dummy lyric to a real one.