We try to keep Krita Manual always up to date. It takes quite a lot of time already since every change to a feature needs to be followed by a change to the manual. Often one needs to make new screenshots etc. There are still outdated pages in the manual, mostly in the Tutorials section, because while it’s not that difficult to remember to change the page about the feature, it’s often not remembered to that some of the tutorials use that feature, too.
With video it would be much much harder to keep it up to date. Every time something change, you basically need to rerecord the video, or at least edit it. That’s enourmous amount of work. It can be used complementarily to the text manual but it would never be as complete as the text manual, because making changes in a video is much harder.
See for example how all animation tutorials got outdated in - I don’t remember which version that was, was it 4.0? - and all existing ones will be outdated again when Krita 5. will be released, needing to create a whole new tutorial series with the new Animation Timeline docker instead of the Krita 4 Animation and Timeline dockers.
And there are smaller examples, like Transform Tool videos talking about five modes instead of existing now six of them… Reference Images docker changed into Reference Images tool… and other things. Every update adds or changes something.