It's interesting, how does one measure the success or population of SL. Is it the number of content creators, or the content consumers.
It surprised me to learn that LL is still selling private regions for the same price, as well as land use fees, as they were 9 years ago.
Ultimately you are right, I think learning blender is still the way to go as creating a mesh AV for SL or one for (the next big VR thing) is likely going to be quite similar in the tools we use.