I think we are actually discussing two very different questions in this thread:
(1) Is having moss on the top layer of your soil harmful/beneficial (aside from aesthetic benefits)?
(2) Is moss growing on your soil a sign of something good/bad with your soil/environment?
Don't assume that what works for Ryan Neil in Portland, OR (43 inches of rain per year) will also work for your trees, depending on where you live and what you use for soil, where you get your water, etc. Ryan uses a 100% inorganic soil mix, gets great soil drainage, and lives in a rain forest with high rainfall and high humidity (average 144 days of sun per year). It would be difficult to NOT grow moss on his soil.
Conversely, consider my last location in Orange County, CA (14 inches of rain per year) with no rainfall for nine months straight every year. If I saw moss growing on ANY of my soil, it was usually a sign of something bad - because it meant I had soil that was remaining saturated in desert humidity (average 278 days of sun per year - almost TWICE as much as in Portland). Additionally, because I was forced to use highly alkaline irrigation water and moss prefers acidic growing conditions, it was a sign that SOMETHING was lowering soil pH. That something could mean an accidental over-application of soil acidifier, an area of over-application of organic fertilizer, etc.
So for me it wasn't a question of whether I
wanted moss to grow... but what moss meant if I saw it growing

For Southern California shows people don't show up with moss naturally growing on their soil. They grow moss separately in controlled conditions, place it on their soil for the show, and then remove it as soon as the show is over.
Often when I see moss on soil (from someone other than Ryan) it is an indication of poor drainage and/or high organic levels. If you look at the OP's tree, I don't see any bonsai soil. I see black organic soil akin to potting soil, and a tree that looks (to me) like it is staying too wet.