This seems like a tough comparison to make, in general. This comparison would favor a BEV only when a trip is greater than the REx range but less than the BEV range. The comparison seems certain to favor a REx most of the time, but at the considerable costs of a higher initial price, additional complexity, additional maintenance, greater weight, less interior space in some cases, etc. To some of us, this trade-off just isn't compelling.
Certainly, those i3 REx owners who frequently drive farther than the range of an i3 BEV and who would not want to stop to charge a BEV sufficiently to complete their journey would drive a REx more electric miles than a BEV. When stopping to charge, some people think that this means stopping to charge to full, but even with an L2 charger, one might need to charge for only 15 minutes to add enough charge to complete one's journey.
However, those of us who rarely drive farther than AER of a REx would drive the same distance in a BEV. I do occasionally drive farther than the AER of a REx but less than the range of our BEV, so I likely drive more electric distance in our BEV than I would in a REx. We have once driven far enough to cause my wife to suffer from extreme range anxiety, so we stopped for 15 minutes at our BMW dealer to charge enough to make her comfortable that we could make it home without being stranded (I think we could have made it