The failure mode is that people unfamiliar with a subject aren't able to distinguish careful analysis from bullshit. However the second failure mode where someone pointing that out is assumed to be calling people stupid is a longstanding wetware bug.

chatGPT voice app can already talk in languages Duolingo doesn't have and will never have on their old path.

They obviously had to do this. It is already over for Duolingo. All we really need is some kind of Anki deck generator with audio and that plus the language model to have conversations with, it is over. They will look like a childish relic of the past.

Grammar lessons are also critical, especially well spaced for when you need to learn them.

Ironically Duolingo removed all of that in the simplification and gameification recently.