Actually, it still is useful. You don't all have to be flying at the same time. Send the melee guys first to find a spot, then break concentration to send the archer, then the spell casters. Just because you can only do one at a time doesn't mean it won't work.
Why am I giving you these ideas? Don't listen to me. You really want to take on the Xanathar. Nothing could go wrong there. Promise.
Sent from my iPad using EN World