"Why do people bring up stressed and unstressed syllables when it comes to setting the durations of the lyrics? Don't we have control over where we choose to stress or not stress syllables? (as hinted at in many of the answers)" Not sure what you mean, but if I understand it right - no, we don't. Stressed and unstressed syllables are inherent to each word, it's part of the language, you can't choose another syllable to place the stress.
When writing a song, stressed syllables belong on the downbeats. Otherwise the song won't flow right and will be awkward for both singer and listener. You h…