It always struck me that back then Hakkai could've taken off his limiters to stop Seiten Tasei, but he chose not to, or didn't even consider it as an option.

Didn't buy this month's ZS, but Hakkai says something to the effect that he didn't try to stop Gokuu before because he was too far away. Not that that makes much sense at all, but hey, if he can lose his eye twice, I'm willing to let that one go too;-)