I’ll be checking over the subtitles anyway, generating just saves a bunch of time before a full pass over it. [...] The editing for the subs generation looks to be as much work as just transcribing a handful of frames at a time.

Sorry I'm confused, which is it?

doing this as a favour [...] Honestly I hate the style haha

I'm probably out of line for saying this but I recommend you reconsider.

You may already have the answer from the other comments - but specifically for subtitle transcription, I've used whisper and set it to output directly into SRT, which I could then import directly into kdenlive or VLC or whatever, with timecodes and everything. It seemed accurate enough that the editing of the subs afterwards was almost non-existant.

I can't remember how I installed Whisper in the first place, but I know (from pressing the up arrow in terminal 50 times) that the command I used was:

whisper FILENAME.MP3 --model medium.en --language English --output_format srt

I was surprised/terrified how accurate the output was - and this was a variety of accents from Northern England and rural Scotland. A few minutes of correcting mistakes only.