The R25 Ultra brings 25 Nm and Moza's newest motor, and scores higher on our overall rubric; the SC2 Sport is $80 cheaper with Simucube's class-leading build and True Drive but only 17 Nm. So you are weighing more torque and a higher score against Simucube's build at a lower price.
For most buyers wanting flagship torque, the R25 Ultra is the stronger pick and not much dearer. The SC2 Sport is the choice if you specifically want into Simucube's build and software and are happy with 17 Nm - it is a superb base, just less torque for the money here.