This is an issue if it’s unsupervised, but the transcription models are good enough now that with oversight then they’re usually useful: checking and correcting the AI generated transcription is almost always quicker than transcribing entirely by hand.
If we approach tasks like these assuming that they are error-prone regardless whether they are done by human or machine, and will always need some oversight and verification, then the AI tools can be very helpful in very non-miraculous ways. I think it was Jason Koebler said in a recent 404 podcast that at Vice he used to transcribe every word of every interview he did as a journalist, but now transcribes everything with AI and has saved hundreds of work hours doing so, but he still manually checks every transcript to verify it.
For what it’s worth I doubt the add-on is doing any translation or sending the youtube subtitles to any other servers. Youtube auto generates translations for videos in loads of languages and then offers subtitles only in the user’s language, so the add-on will just be accessing those already existing .SRT files off of YouTube’s servers which you can’t normally see and displaying them.