I think there might be an illusion of creativity rather than actual creativity. I’m sure associating accents with traits is useful but it’s kind of lazy to me. For example, since it was talked about earlier, Hagrid in Harry Potter has a West County accent. This makes him a loveable oaf because the accent comes through as meandering and gruff. It’s vivid but it isn’t clever.
I read a decent-ish amount and I don’t often come across this type of “old speech” or “rough speech” outside Young Adult. That’s probably why it seems less varied or original than in Japanese because English usually can’t do it at all.
I don’t think good authors need to use that sort of thing because the dialogue should speak for itself without tropes. Fer example, if t’only way thi can mek a Yorkshuhman cum through ont’page is ba butchain’ English then t’dialogue probably in’t an’cop int’fist place.