I wouldn't say that entirely, open communications do help a LOT in the end game, but your eyes should be glued to the health bars of your entire group.
How Binding Coil of Bahamut works on the main bosses of each turn is, one person dies, it's more or less a wipe.
It's possible to get a dps back up, but if a tank or healer dies, it's over, retry.
So yeah, speaking does help a lot, but it's not hard to take 1 second out and see the white mage is out of mana just about, not that Tyler or myself every have mana problems.
But when I say I generally hate a class or someone, they have ******
Lately also in random parties, all the healers rather try to be dps instead of heal and oh dear god... you have no idea...