The safepoint_check_never locks should be lower in the lock rank hierarchy and shouldn't be nonleaf.  Making them nonleaf implies that other safepoint checking locks can be taken out while they are held, which sort of invites the question of why these locks are safepoint_check_never.  If they can't safepoint, why can we safepoint while they're being held?
I think the ranks were chosen for these locks out of convenience, ie, was just a guess and it worked because other locks taken after these locks were also safepoint_check_never locks.