RDA was beaten by wrestlers at LW (Guida, Khabib), and we haven't seen him deal with a pure wrestler in years. Some say RDA's wrestling/TDD has improved a lot, but I don't think there's evidence. He's ragdolled a few guys like Pettis, but Pettis has very weak wrestling. Since Khabib, he's fought a few guys with decent wrestling (Bendo, Alvarez, TFerg), but 2 of those fights ended in 1st round KOs and Ferguson isn't a traditional wrestler at all. His style is nothing like Colby, Usman, Kevin Lee, Khabib, etc.
All that to say it's a pretty unpredictable fight in my book. I don't get the "RDA can't lose" stuff, but I'm not 100% confident in Colby either.