To me this is fairly dependent on how fast the speaker speaks. Most of the times 1.25x works well. Sometimes 1.5x is too fast.

I find this true on podcasts; I'm normally a 1.3-1.5x person listening to podcasts, except "No Such Thing as a Fish". That one I go slower on, just because they seem to talk quite quickly, comparatively.

I think the slowness of the videos is for non-english speakers. Meaning people who can understand english to a point, but aren't using english every day.

Some years ago when I used to play games there was these awesome guides to some hard challenges a guy made where he was speaking pretty fast because there was a lot to cover and it was narrated over live footage. It was perfectly understandable to me, but the comment section was full of complains about the speed and how it was too hard to follow. This to me suggests that most of people would prefer if you paused the action to make your point slowly and after that continued with the footage.

Wait, you can also slow down YouTube videos, can't you ?

Yeah but it sounds like shut then since there are fewer samples per second of Playback.

yes, but that's an option you need to select. Normal people aren't going to even try searching for an option like that. Also it was 8 years ago, so I don't know if that was an option back then and in any case that would slowdown the footage as well.

I also have this problem (it might be related to my ADHD). 2x speed (with occasional pauses/rewinds) works much better for my retention; I've often explicitly noticed myself not paying attention and learning nothing at 1x.