Well, as someone who could possibly be a super-duper English editor (if I wasn’t so put off by the whole process of becoming one), I have to say that not using Korean honorifics, but using something like “Big Bro” or “Big Sis” or “Mister” implies (to me) impolite casualness and not polite respect.
A “correct” English rendering in my book would be “Honored Older Brother,” “Honored Older Sister,” and “Honored Older Man I Want To Show Respect To,” but what a way to clog up a screen.
And if people so addicted to K-dramas that they spend 50% of their waking lives SUBBING AND SEGMENTING AND EDITING . . . don’t get that other addicts already know bout them honorifics . . . then all I can do is give all of them a Scooby badge . . . Ruh-roh!
(from Business Insider website, “Scooby Doo’s real name isn’t really Scoobert Doobert”)