Garuda is definitely a DPS check. With high enough DPS pre-AB, you can still easily skip the 2nd phase...which is probably where most Garuda parties have issues. If you get her HP low enough following the Aerial Blast, she will either summon the 2 adds or go to the plume/rotating whirlwind phase...both of which are not that hard to react to. The middle phase in my opinion is harder than either of those 2 and where low DPS groups are probably wiping.

A side note to those needing this for relics, it needs to be a win with 0 deaths to get the item.