I am using TBSync for Office 365. It only works one way. Events in my O365 calendar show up in my TB calendar, but not vice versa.
RSVP doesn't also work right now from the TB calendar. Author claims he might fix it by the end of the year.
RSVP doesn't also work right now from the TB calendar. Author claims he might fix it by the end of the year.
Contrary to your experience, I was even able to create events from thunderbird that would show up on O365. They only show up on sync however (which does not seems to be automatic, only on timer). Maybe that's the reason why it did not appear to work for you?