Enjoy my other Final Fantasy X HD Remaster cutscenes here: • Final Fantasy X HD Rem... All copyrights go to Final Fantasy X HD Remaster and Square Enix.
Notice the ship has "yevon" text, yevon is acctually a religion based from the bevelle peoples fear of yu yevon the zanarkand guy who made sin, making this airship a zanarkand one.
The Hymn of fayth actually involves the use of prayer, which in FFX is magic itself. So, yes it actually would reach that high even without every single person singing in unison. As long as the prayer is strong enough, the magic will form.