This is a straight ladder decision within one brand. Both run MOZA Pit House, both take the same wheels, and on our rubric they land close together - so you are really buying torque and chassis, not a different experience. The R12 V2 is the base that made the mid tier recalculate: 12 Nm, crisp kerb detail, every bump coming through, for the price most brands want for a wheel and base together. For a lot of people that is the end of the conversation.
The R16 V2 exists for the driver who wants more. Sixteen Newton-metres at $699 is Moza charging upper-mid money for what some brands would badge as a flagship number, and the chassis steps up to match - it is the rung that turned the R-range from a couple of bases into a real ladder. The extra 4 Nm is not just a bigger number; it is headroom, the room for forces to keep climbing in heavy open-wheel and high-downforce cars before they clip. If you have ever felt a 12 Nm base run out of top end, that is what the 16 buys back.
So the real question is whether you need it. Twelve Nm is comfortably enough for most driving, and the $300 you save on the R12 V2 goes a long way towards a better wheel or pedals - which usually matters more to your pace than the last few Newton-metres. Step up to the R16 V2 if you specifically want the headroom and the stiffer build, or you are chasing that flagship feel without paying flagship prices. Either way you are on the same ladder, so nothing you buy now is stranded later.