Experienced healers and such know how to manage mp same as dps with tp, etc.
Songs are there to be sung if or when needed not always a must needed.
Army's Patheon i maybe only ever used it 3 or 4 times as Bard. Twice in a few of my first ever T4 runs back in the day as warior tank asked for it
and maybe once when i was not paying attention to my tp so was out, lol.
Mage's Ballad and Foe Requiem by far are the most useful songs and i also agree some comments people make about Bard being a "support" class, well why do i out dps them even while i have a song active, lol (mainly drgs make those comments at Bards usually)

Foe is used when either a blm or smn are in the group i don't think windbite or venemeous bite is effected, however i truly believe Holy from a whm is