The drag coefficients of even the more recent Teslas are comparable to other vehicles that don’t use retracting door handles, even the GM EV1 from 1999 beats all the Teslas on the table in terms of drag reduction. The door handles may technically be a contributing factor towards their more favorable position on the list, but they’re certainly not necessary and don’t seem to be highly impactful. A large part of Tesla design philosophy and marketing is making their cars seem futuristic and highly advanced through things like motorized door handles and autopilot. Their primary goal is to provide a unique and pleasant user experience “out of the box” and their justification for things like the door handles retracting are almost certainly retroactive.