the Nudds and Dyke's feather paper is not alone in inferring extremely poor flight abilities for _Archaeopteryx_ and _Confuciusornis_. There is the work by Senter on scapular orientation, which showed that neither bird was capable of a complete flight stroke.
Baffling though it is, they were both apparently unable to lift their arms above shoulder level. That kinda sucks.
Then there's the matter of the keel - absurdly small in _Confuciusornis_, non-existent in _Archaeopteryx_.
Bats have no keel at all...That said, the keel of extant birds does not immediately ossify. It stays cartilaginous and unfossilizable for quite some time.