Fucking love that Benfica vid.
It's sang too fast and becomes disjointed. Almost perfectly sang in unison at the right speed in that video.
There's a shelf-life to all songs and they all follow the same rough pattern.
1. They are introduced and, if successful, catch on surprisingly quickly.
2. After half a dozen matches they are at their very best and start to pull in even those supporters who are not usually interested in singing.
3. For 6 months (more or less) the song is at peak performance.
4. Then it speeds up as bad singers fail to breathe when they're singing and cannot tolerate beats or gaps where there is no sound. Good singers (probably the majority) have to follow the shit ones, even though they know the song is being butchered.
5. The degeneration continues and lasts for years until a song becomes literally un-singable and eventually is discarded or simply turns into a music-less chant like PST.
You want to hear YNWA at its finest? Listen to the 1965 Cup Final extra time. (Compare with the fiasco on the Last Day of the Kop where it has become little more than a bellowed chant). FOAR? Benfica. Allez Allez? Man City in the quarters.
There are three ways of fixing this. One is a powerful sound system that dictates the tempo of a song. YNWA at kick off can still be very impressive. Another is a Grupenfuehrer with a loud hailer and drum as happens on the Continent (ugh). The other is a concerted effort by supporters to educate each other. (Spurs have clearly done this with 'When the Cocks go marching in'. It's impressive).