I agree with what you wrote but think Sanders needs to do more.
He needs to use his money and social media to spread his word where the traditional media won’t. For instance why not create interactive web forums where people can ask him questions in real time? Create a Netflix movie about his campaign and or about Bernie himself? Could take us through a day or week or month in the life of Bernie.
Bernie also needs to couch the personal progressive problems in relatable stories. For instance on education, he could use the strong argument that only our children should profit from their education, not for profit companies and politicians.