Nudds and Dyke was that they overestimated the mass of the Archaeopteryx
specimen they examined by a factor of about two, Confusicusornis by about three.
If 20% doesn't matter then I wonder why you bothered adjusting Yalden's
estimate for the body mass of HMN 1880 by 13% (from 271 to 234g). You also
spend some time discussing the relative merits of a pectoralis mass between 5
and 15% of body mass.
Moreover, we would both agree that 20% doesn't matter to extant migratory birds
with highly derived flight apparatus, but modern birds have a lot of spare
capacity. They can stoop at 200 mph, hover in mid air, and fly thousands of
miles! In an animal that is barely capable of aerodynamic locomotion, like any
hypothetical ancestor of birds, 20% could be a crucial difference between
ascending flight and gliding.
I agree that Nudds and Dyke used mass estimates that are too high and rachis
measurements that were too small, and that their conclusions must thus be
reconsidered. But Zheng et al. found that Nudds and Dyke still demonstrated
that both birds had weak rachises compared to extant birds of the same mass. I
still think they flew, but this contribution by Nudds and Dyke suggests that
Confuciusornis probably couldn't pull the miraculous maneuvers (pouncing on
fish and then taking off from the water surface) that kingfishers do today.