I know exactly what you mean. I think the theory here is that DBX is efficient from that supinated RDT posture because the escaped downstrokes are extension plus ulnar deviation, while the upstrokes are just radial deviation. String-hopping on the other hand has built-in muscle reuse (like every pickstroke uses both flexion and extension) and is therefore both slower and with much lower endurance.
That said, I don’t think you’re supposed to do DBX per se, you just practice mixed escape lines from that general form and aim to get things clean.