Its really bad for forward compatibility to be buying EF lenses if you're buying into the RF system brand new. I know Sony's lack of truly native stuff is what kept me from staying with them over time, and thats an issue that's been sorted out.
I guess Canon has the benefit of not caring if people buy EF or RF, but its still not as strong a hook if you're adapting lenses.
I could see video people buying into EF lenses still. The biggest advantage of the adapter is the ability to use ND.