I was going to call this anecdotal evidence based on it never appearing in the top 100 (or so) Nielson rated TV shows for a year, based on the lists for 1984-1995 here[0].
However, it looks like PBS never signed up for Nielson until 2009, so we have limited/no public data on viewership of The Joy of Painting (or Sesame Street, etc for that matter).
http://www.thetvratingsguide.com/2020/02/tvrg-ratings-histor...
Inside the US, never heard of him until later 2000s or so as well. And watched PBS at times.
Did you grow up wealthy in the 80s? Most people didn’t have cable television back then, it was comparatively expensive and not available outside major metropolitan areas. Most people only had a half dozen TV channels or so, and sometimes Bob Ross was the only thing on TV worth watching. Everyone knew who he was.
We were not rich but had basic cable since 1979 or so. Maybe California was ahead on that front. My memory is that it only cost perhaps $10 a month in the 80s.
My experience was that accidentally tuning into Joy of Painting for about 45 seconds was enough to completely hook me (although I was not fully aware of this at the time).
There was a lot less tv in the 80s. If you didn’t have cable, then you just had a handful of channels. I didn’t watch Joy of Painting, but it was pretty hard not to notice the painting Afro guy when flipping through the extremely limited number of channels most people had access to.
There's a lot of TV shows out there, even in the 80s and 90s, and plenty of ways for celebrities to have their image and reputation bolstered. Ratings aren't reliable in trying to measure someone's notoriety.
Growing up in the late 80s/90s, and mostly outside of the US, I can't remember a time when I didn't know who Bob Ross was.