> ability to tolerate potentially biting criticism that comes with it
I wonder if this is the issue really. Some people can't take criticism unless wrapped in sugar. If it's really, and especially if it comes with potential alternatives it should be socially fine, but it's not.
Another aspect is how the rest of the team felt over time. They probably built up deep resentment towards this person which ultimately only fed back into the cycle. So whether or not they were aware of it, they probably formed a clique to team up against this person, again only exacerbating the core issue.
I wonder if this is the issue really. Some people can't take criticism unless wrapped in sugar. If it's really, and especially if it comes with potential alternatives it should be socially fine, but it's not.