I'm puzzled by this statement. Do you think of resiliency as waste? That twitter would have been fine without it?

The article makes a point that the reason Twitter is running ok on 20% of personnel at this moment is exactly because it was build to be resilient, not because the personnel was bloated. A large part of this so called bloat, the 80%, was responsible for Twitter to be running right now. Calling this bloat implies it is actually not important for Twitter to be available all the time (or at all).