> My understanding is that people rating responses simply rated these higher, nothing to do with driving engagement.
That happens to be a distinction without a consequence. If the people rating are voluntary users, then the more engaged users are going to have more weight in the ratings, simply because they vote more. The ratings will therefore statistically skew towards higher engagement.
I think that's a very important distinction, because it speaks to the intentions of the creators. It's not being designed this way, it's an accident.
I believe you would have to assume an inordinate amount of naivite, bordering on stupidity, by the developers to suggest they didn't know this is exactly the outcome. They are statistics experts. They know about survivorship bias.
Of course they were aware of the possibility, but there's not many good measures of quality.