> A few hours later in a biweekly update meeting with said client, we mentioned having finished the feature. The client's project manager responded that actually the person who cared about that feature left the company, so it is no longer in scope. Then they erased it from the project tracking record, and in the same breath complained that so little progress had been made against the other objectives.

Actually, I don't see here an issue with doing "agile" or "waterfall". It's a communications issue. Either someone at "Big Mean Secret" company did not manage communications with the client properly, or the client didn't bother to communicate properly when given the opportunity.

Either way, using a "waterfall" methodology would not have helped here. It can be said that maybe "agile" "done right" would have solved this issue, but when is "agile" ever "done right"?

(The last sentence was an over generalization of course)