The unusual part here is that the newer base is the more expensive one, the opposite of what happened with MOZA's R21 and R21 Ultra. The SC2 Pro has been the reference flagship for years - build quality nobody has beaten, True Drive software polish, and the base every review still uses as the yardstick. The SC3 Pro is the proper successor, with a newer motor, refined thermals and Simucube Tuner 3.0 at the centre of it. On our rubric they average out identical: the SC3 takes top marks for fidelity, the SC2 holds a slight edge on reliability from years of proven service.
So you are not choosing between a good base and a better one - you are choosing between a proven flagship and a newer, dearer flagship that is a touch cleaner at the very top. The SC2 Pro's 25 Nm hits slightly above the practical sweet spot for most sim racers, the wireless wheel tech is impressive with no latency penalty, and four years in it still reads as the pinnacle to a lot of owners. Spending the extra ~$480 on the SC3 Pro buys you the newest motor and the last increment of refinement, not a transformation.
My take: unless you want the current-generation badge or you are chasing the absolute top of the fidelity scale, the SC2 Pro is the smarter money. It is one of the best direct drive bases ever made and it now sits at a serious discount to its successor. The SC3 Pro is the pick if you are building a no-compromise rig, you want the base with nothing above it, and the price is not the deciding factor. Both are unimpeachable hardware - the SC3's only real obstacle is what it costs next to the base it replaces.