I don't know if anybody realized this yet, because they're grinding on one character first. But you can grab every artifact from Tyra and attune them. I--and a lot of others I'm sure--initially believed you can only get one Iron Lords' Legacy a week, which equates to one artifact a week. However you can indeed get three a week. I do still believe that attuning all eight artifacts in the Iron Temple will unlock something. Maybe a quest, or a secret room in the temple. Who knows? So be sure your others characters are up to speed to get their own artifacts.