Some British accents, in particular outside of London, can be almost unintelligible to general English speakers.
There is nothing intrinsically neutral about the British accent, it's more a matter of diction from the speaker. I would also not consider the OpenAI accents as neutral American, feels more like "Young Californian adult woman" accent to me.
You don’t seem to have a point. Thick accents are unintelligible regardless of source.
The UK has more distinct accents than the US. However RP English, which was popular in an American form as “mid Atlantic” last century, is almost impossible for any English speaker to misconstrue thanks to its emphasis on clear diction. British actors have been proving that in the US for over a century. No one needs subtitles to understand Hugh Grant. Standard US accents frequently fail the merry, marry, Mary test and are worse overall.
Even us Americans know this. The classic, original, beloved voice of the NY subway was a British guy faking a “flat” American accent.
There is nothing intrinsically neutral about the British accent, it's more a matter of diction from the speaker. I would also not consider the OpenAI accents as neutral American, feels more like "Young Californian adult woman" accent to me.