The R21 Ultra is a lot of flagship for the money: 21 Nm on Moza's newest motor, $300 below the Podium DD1, and higher on our rubric. It turned the R-range into a proper flagship line. The Podium DD1's answer is Xbox support and the Fanatec ecosystem, the reasons to pay more.
So on PC, the R21 Ultra wins comfortably on torque, refinement and price. The Podium DD1 is the pick only if you need Xbox or you are committed to Fanatec's rim catalogue - otherwise the MOZA is the stronger and cheaper flagship.