> The Star left cluster are primarily operations that pair the left hand on the keys with the right hand on the mouse.

Sure (this is demonstrated in the linked video, for instance) but the ZXCV group is pretty similar in that respect. Even for operations which involve the mouse it's preferable to drag only one hand far away from its home position, rather than both of them. (Especially since the video evidence https://www.youtube.com/watch?v=Cn4vC80Pv6Q seems to suggest that Star users tended to move their left hand only after making the mouse selection, instead of prepositioning it.) And the Star's Undo key, which presumably doesn't require help from mouse input and is likely to be needed after a non-mouse action, isn't placed any more conveniently near the home row: it's simply in the right side-cluster rather than the left one.