While I think I agree with your geneal stance, I also believe 'no knowledge is lost' is pure hyperbole.

Aside from many different quasi-documentaries, video essayists and slice-of-life bloggers (whose content is surely backed up on other platforms or by data hoarders) the sheer amount of tacit knowledge of small computer/electronics/hardware repairs and similar, especially in smaller channels, is in no way either 'not knowledge' or not 'lost' should the platform go up in flames tomorrow.