What this stack of flexifoils shows is how weak the kites are when crowded together, the high pressure wanted under a kite cancelled by the low pressure over a kite below. That’s why one skinny guy can fly them all, and they fly very slowly compared to a single flexi, which helps the pilot manage. An old heuristic is to space kites in a power stack at least 3 Wing Spans apart, and there is still considerable loss of power. A properly staggered multiwing has a different (trailing) geometry than a (vertical) stack, and even then may not beat one good kite matched to conditions. That this stack may do a low-radius loop does not offset the other losses.