Thanks for bringing up that LinusTechsTips video - I'll try and track it down. I would not have expected that conclusion. I've already said in another comment on this thread that I'd expect the opposite!

This seems like the video that the GP post was referring to: https://www.youtube.com/watch?v=AF2O4l1JprI

Linus is surprised that fast charging does not heat the battery as much as expected.

I interpreted that "length of charging doing more damage than fast charging" meant that slow charging was worse, because the battery spends more time charging, but I don't think this is stated in the video. In the video, Linus confirms that it is the high state of charge that does the damage and that trying to keep the state of charge as close to 50ish % is best. The conclusion that fast charging is better for the battery, is because you are more likely to do it when awake, and can stop the charging once it reaches whatever percentage you require (but the damage really starts to increase above 80%.