I like the link to the 2018 stats.. thanks for That!
I disagree only in one statement you made: "Might mean you are getting in on the bottom of a trend - or it might mean small businesses have found it adds little to nothing to sales."
I personally draw a LOT of sales from my YouTube Channel. I think, 9% of small business are in it... because 91% do not know what it can do for them OR they do not want to make the investment for it. Which is what I would call a MASSIVE opportunity.
If the same article came out 20 years ago about websites that said only 9% have websites, your "bottom of the trend" statement would be completly wrong (in hindsight); but not necessarily untrue based on the state of the internet and internet users at the moment. Is also possible that only 9% of the small business buyers use YouTube, but if as the trend moves up.. so will the adoption.
I could also be wrong in the way I am reading if your statement "bottom of the trend" means being too early or too being late.. would love your clarification on that