I'm not sure about whisper, but find YT subtitles pretty poor.

I generally watch videos on 1.5-2x speed (depending on speed of person talking).

I also turn on subtitles in case I miss a word due to the speed, and find it very random at times.

I always thought YT missed a major opportunity: let users submit corrections to the subtitles (probably by clicking on the words it got wrong).

It would have made the experience so much better for everyone who uses subtitles.

Not all videos have subtitles. I do initially run yt-dlp with the extract subtitles parameter, then I check whether those subtitles were downloaded, then if not, I run whisper.