One of the many 'technical communications' courses (think high school English class, but post -secondary) I've taken over the years had a short section on this, although it was more on slide presentations the lesson still applies. One of the worst things you can do is a presentation where you just narrate what's on screen. What should be done is visually show the non-verbal items, outline, etc. while covering the less critical information through speaking.
in the end the challenge of "both" is to avoid reusing 1:1 the material between both mediums, but it is more work. ;)
With the obvious consequence that slide sets will be used as post presentation reference material and stuffed with too much content to really serve the presentation itself. I have seen some reaaaaly bad slide sets of people who seriously hate white space...
Personally, I am a supporter of the approach of using the medium that fits the objective best - and just to be clear, that means if the picture element of a video doesn't contribute to content delivery, don't use it; if the audio doesn't have an enhancing effect, don't use it. Text is human reader skimmable, provides an adaptable reading speed and is browser/search engine searchable. :)
That said, given we are in three digit numbers of updates and these discussion has come up repeatedly, I seriously doubt that the workflow will now change. Which makes this side discussion somewhat pointless.