((Warning: Serious Weiss fanboying inbound.))
The calamity in Vale has been a subject of study for the last three decades with particular focus on its principal mitigating causes, especially among the proponents of the 'Great Man Theory' of history, whereupon pivotal moments in history are caused by one man, and so attempt to apply it to this situation. Particular focus is placed upon the Huntress team RWBY, of which its various members are held responsible.
If I were to apply this theory, my own opinion in this matter is that the Huntress Weiss Schnee holds a majority of the responsibility for halting the calamity in tandem with the rest of the team. Her skills were essential in halting the calamity and reducing Grimm-inflicted casualties, in particular her mastery of Dust manipulation, and without which they could not have done so. In addition, her influence was second to none in helping to create the strategies utilised by her leader and her teammates during the Breach, hence why I place Miss Schnee as a principal factor in halting the calamity.