The driveshafts are not being turned by a belt when BSG is active.I suspect the eTorque part of the mild-hybrid system is what really makes the 2.0 turbo feel so good. The Wrangler doesn't need a smaller sequential turbo, because at low RPM, there's an electric motor twisting the driveshaft with a belt.
Now, you can get the 2.0L engine without eTorque, and this C&D article reads, " It's difficult to detect any difference between the 2.0-liter with electrical assist or without," but how can that be, when you're missing 70 lb-ft of instantaneous eTorque? But the same article does also read, "the automatic [transmission] is programmed to help mask any hint of turbo lag as the engine revs".
Hmmm. My only electric vehicle experience is with indoor go-karts, motorcycles, and bicycles, and it feels amazing how that instant motor torque scoots you up to speed. That's why I thought the electrical part of the eTorque system deserved more credit.