I had a friend that required reconstructive surgery on her hand from a rescued Moluccan Cockatoo. Birds that have bills designed by evolution to crush large nuts absolutely have the ability to inflict some serious damage to soft human flesh. Any bird can be aggressive. It's best not to make blanket statements unless it is qualified by something like "in my experience" or "in my opinion."
I wouldn't say all Hyacinth Macaws are aggressive, but I've also had a friend with a pair that worked in concert to let themselves out of their flight/yard of the breeding barn and into their indoor enclosure to defend their nest which resulted in them taking one of his fingers completely off. I also had another friend with a pair of Goffins that regularly got out of their cage and would chew threw the nestboxes of other birds on eggs or chicks to kill the other birds in that cage. And yet another friend who had a female Greater Sulphur Crested that was on three separate occasions nearly killed by three different males she was paired with. The fourth male attempted to bully her and she killed him. The fifth died of natural causes and she now goes broody every year on her infertile eggs before plucking one feather and feeding it for several weeks before giving up on children for the year.