The head of Instagrams public policy is very correct when she states: Teens are exceptionally creative. Assholes and bullies have always existed, 25 years ago at least you had a respite at home after school, but now social media makes victims available 24-7.
Not to sound defeatist, but I don't think social media can exist while preventing bullying. For the victims it's binary, either they're being bullied or they're not, so social media needs to prevent 100% for bullying and that is not going to happen, people will always find a way to be assholes.
In my mind the effort is misplaced, at least for teenagers who often know the bully. It's the schools and parents that need to take action, not some random faceless US corporation.
For 100% online bullying... I don't think there's away around that. You can try to reduce the amount, but you won't be able to eliminate it.