Yamamoto says that the Zanka No Tachi CAN REACH 15.000.000 in this case the Zanka no Tachi against Royd are not in 15.000.000 but can reach.
If he want to destroy the Soul Society he just Increases his degress to reach 15 million, and he throws it out the reiatsu Causing an explosion like he did in shikai state.
Sword Royd without touching the Yamamoto was intact, but when he struck Yamamoto without even he used the flames covered the body, she just vanished just touching the skin Yamamto, now you see the difference in just being close and touching the yamamoto?
yamamoto with reaitsu released it houses a huge area in the form shikai, so imagine the state bankai probably reaches all sereitei or even more.
summarizing what Yamamoto did not use all his power not to destroy your home.
and perhaps still has the hand, northwest, northeast, southwest and southeast.