I'm not entirely sure what channel keywords do, I believe it's to help give a better SEO picture of your channel overall rather than just relying on describing your videos with tage. In the channel tags, you're allowed to put in multiple one word or more tags and it's perfectly fine, doing so in your about me description would be seen as keyword stuffing.
In the VIDEO TAGS, it helps put your video front of eyes that might be more interested in seeing your videos.
Even though YouTube says tags aren't that important anymore, I beg to differ. Some channels won't even make it into suggested, so if you can make search your highest traffic source instead of channel, that means at least people are LOOKING for a particular topic, your videos will show up, rather than HOPING a video will show up in discovery.
My opinion is TAGS get you to the front door. A good title and thumbnail and topic, opens the door to recommended and suggested. So good quality tags to me are still important.
Also, know how to read your traffic source impressions. that will show how much of an impact your tags are making overall.