Nowadays, we do actually have published research that backs this up, but with this as in many other cases, experienced teachers at the chalk face didn’t need research to tell them what commonsense already had.
The research isn’t clear on that point and it take a lot of effort to draw the conclusions you’ve drawn. What make you think it’s “commonsense”?
Because the research is clear, and it doesn’t take any real effort at all. Sorry, I don’t know how to respond to that any other way. You’re acting as if this is complicated. It’s really quite simple and straightforward. Maybe that’s because of my experience and qualifications, but I really don’t think it is.