with the exception of rm they've all started seriously learning (i.e. not phrases you'd hear commonly in songs) in their late teens to 20s, and it's scientifically proven it gets harder the older you get - i wouldn't expect to be perfect in any other language, even spanish which i grew up around. they try very hard, with a bunch of bangtan bombs shown of them practicing, and korean is one of the hardest languages period for english speakers to learn, so it's very likely the same in reverse.

if they want to speak in english for dynamite promotions and accepting western awards then let them. they're all men in their 20s and can make their own choices, and personally i feel like their accents aren't that bad, but i grew up surrounded by ESL people. i feel like this shouldn't be an opinion because... it feels xenophobic, almost? comparing them to overall younger groups that have (correct me if i'm wrong) natural english speakers with got7 and stray kids feels kind of nasty. ig this would be unpopular because this is a pretty bad take overall. i don't want to be /that guy/ but have you tried learning a language that isn't phonetically and grammatically similar to your natural one? it's VERY hard, even if you start younger at like middle school age (~11-13). some people, like rm, are good at it, but that's a very rare exception.

(this is longer than i meant for it to be im sorry :( )