That is not the case here - I never encountered this with whisper-large-v3 or similar ASR models. Part of the reason, I guess, is that those subs are burnt into the movie, which makes them hard to extract. Standalone subs need the corresponding video resource to match the audio and text. So nothing is better than YouTube videos which are already aligned.
At least for English, those "fansubs" aren't typically burnt into the movie*, but ride along in the video container (MP4/MKV) as subtitle streams. They can typically be extracted as SRT files (plain text with sentence level timestamps).
*Although it used to be more common for AVI files in the olden days.
I have also found them inside mkvs as the subtitle track. I think SRT was the default because most content was ripped from DVD/BD, but now most of the content is from streaming sources and you need to convert the subtitles anyway.
