I've never been able to figure out what's going on with the sword in the stone at the beastkin capital. Am I missing some hidden requirement to be able to pull it out?

You just need a lot of strength. Like, over 120 kind of strength.

You need 175 physical attribute, including equipment and class bonuses. Things like worker's outfits and gauntlets do add up, but you will probably still need to get a physical class or two. And no, you can't have someone else pull the sword.