The blame is on tsunade, pain didn't launch ST before invading the leaf. Heck tsunade could have prevented this by taking down pain immediately, if she had the combat oriented style as the other hokage. Tsunade was the hokage, and under her authority the village was obliterated and countless deaths occurred under her leadership. Trying to replace tsunade with past hokage doesn't ignore tsunade's failure in protecting the village, nor does it prove the other hokage could have protect the village worse than her. All types of factors would influence how the other kages would deal with Pein besides combat skills. Intel and speed/reaction to the event also play a huge role, something that was lacking in the this event. Heck 100% kurama TBB might have completely destroyed the village also, but minato prevented that, largely due to his combat skills and reaction to the event.