This is the fight at the top of the PC market, and it splits cleanly. The R25 Ultra gives you 25 Nm and Moza's newest motor for the price most rivals charge for 16 to 18 Nm - it is the value flagship, and it finally answered whether Moza could compete on refinement rather than just price. The SC3 Pro answers a different question: it is the fidelity and build reference, top of our rubric on both, the base that sets the ceiling others are measured against.
So you are choosing between more torque for less money and the last increment of polish for more. On our scoring the R25 Ultra is a hair ahead on the overall average, carried by value, while the SC3 Pro takes the two axes that matter most to purists - fidelity and build - and simply maxes them. Neither is wrong; they are aimed at different buyers. The Moza is the pragmatist's flagship, the Simucube the perfectionist's.
For most people spending flagship money, I would take the R25 Ultra - it delivers the torque and most of the refinement for meaningfully less, and the ecosystem around it is strong. The SC3 Pro is the pick when you want the best-feeling, best-built base in the class and the extra outlay does not change your decision. Both are proper flagship hardware; the R25 Ultra just gives you more of it per pound.