I used to attend a song-writing group a few years back, which was "mentored" by a musician from a well-known "indie" band. It was a totally different approach to song-writing from what I had been doing on my own: I nearly always wrote the words first, then the tune, then added chords that I knew I could play, and sometimes there would be an instrumental break - usually just an extra run through the main tune or chorus tune.
But in this group it was - write a chord sequence first, then see if you can fit a tune on to those chords, a middle eight, then words last! But yes, middle eights, nines, tens, were definitely required!