What the vector-space data gets right, and what the human commentary tends not to, is the idea that accents are a complex statistical distribution. You should be careful about the concept of a "default" or "neutral" accent. Telecommunications has spent the 20th century flattening accents together, as has accent discrimination. There's always the tendency for people to say "my accent is the neutral standard against which all others should be measured".
For sure, and I don't think we ever use the term default or neutral. The "the American English accent of our expert accent coach Eliza" is just that -- it's one accent.
As a learning platform that provides instruction to our users, we do need to set some kind of direction in our pedagogy, but we 100% recognize that there isn't just 1 American English accent, and there's lots of variance.
Well, no. That would also measure what accents someone has the most exposure to, which doesn't necessarily reflect its "absolute intelligibility", but rather its popularity. Popularity and optimality are not the same thing. You would first need to measure if an accent's popularity is a result of its optimality to make the claim that your measure is accurate.
> Popularity and optimality are not the same thing.
Yes they are. If we lived in a world where Australia was a world superpower we might be having this conversation upside down and with r’s where there shouldn’t be any, but we don’t. Every student wants to learn to speak with an American accent because it has the highest level of intelligibility owing to exposure via cinema, music, expatriate communities, etc.
Then you're not describing mutual intelligibility:
> In linguistics, mutual intelligibility is a relationship between different but related language varieties in which speakers of the different varieties can readily understand each other without prior familiarity or special effort.
