Peter Cushing’s and most of Harrison Ford’s performance would be totally fine in the modern age because the the line delivery is literally timeless. But certain parts of Hamill and Fisher’s performance have line delivery that was abundant in that time. The dialogue doesn’t help much either as some of it has a 70’s vibe to it. But it’s not as though SW is the only film in the OT with that problem; ESB has it to. The whole “Why you half witted scruffy looking nerf herder”…“Who’s scruffy looking” exchange wouldn’t work in the present.