Have you had any contact with DO's support or security team prior to this? You are correct that companies frequently ignore or downplay reports but it's nice to at least make that first attempt for each new find (per company). This is only ever done as a courtesy, I'm not saying you must or even that you should have here.

Remember, it's just another nerd out there somewhere who receives your report. Sometimes they are super stoked to have it and will be very responsive. This can be more satisfying than a public disclosure without first contacting the company.