We don't know everything that happened there but having an alacren that actually knows what to do on that encounter makes it significantly easier and stops people from going down. Even with my guildies, if I have an alac-in-training, I usually relog as second alac for that encounter. Yes, I'd drop a dps slot for a good alac.
And its not for alacrity ^^ I mean alac uptime doesnt matter much there, anything is fine as long as your primary job is done.
Primary Job: use ventari bubble to block projectiles and do good cc ^^ izi...
That way your team can stay stacked and clear the content without too much chaos ^^
Alac tip: know what to bring to each encounter, ask your team if unclear. There is a spreadsheet floating around the internets somewhere.
edit: it's here: https://docs.google.com/spreadsheets/d/109oGym5u-eDzd2Mi-kmrYQkf4RRKNLCSMzI6Uri-BFA/edit#gid=341613541
(ty Jani)