nobody has evidence... except MAYBE wotc... so if you are asking on a thread on enworld for better get used to being disappointed.
Well, I live for disappointment!
...but, we have a number of indicators of the popularity of 5e. We have a number of indicators of the demographics of 5e. We have a number of indicators about the sales of 5e.
There's not perfect information- but there's a lot of good information. I will note that no one seems very interested in providing any information that would support their belief that so many people are unhappy with the game and that new players are leaving in large quantities (which is ... certain an assertion).
Personally, I have been assuming for some time that this is another bubble, similar to the one in the early 80s. To date, I have been wrong.