Maybe not relevant as I no longer play…but this has also been refuted by many, myself included. I ran 2x tc 20 for 18 months continuously, the other 2 intermittently for a year. My rewards? Precisely 2 5* cards. Elena and Elkanen. Probably an extreme example of bad luck, but it happens, and happens to a lot of players.
I think the proposed odds of getting a 5* card (put at roughly 4 or 5% by the wider community) is an average and, as such, requires both your and my example to be anywhere near accurate. 