In the notification settings there are advanced filters to remove notifications from accounts that you don't follow, don't follow you, new accounts, accounts that have unconfirmed contact information. I don't know any other platform that offers so much control. I have been lucky to never experience this type of abuse but if I were under attack I would apply advanced filters until the storm passes. Twitter could certainly do better (and could take more of a stand against cut and dry abuse), but in the meantime there are tools in the hands of users today to take control of unwanted notifications.