RE: YT/KMP FW-190A
1.) cost/ease of development/manufacture: It would have cost no more, nor been any more difficult to develop or manufacture had the manufacturer used accurate 3 views which are readily available for the Fw190, up to and including actual factory blueprints.
2.) copyright: the Fw190 is under no such regulations. Since the manufactures are typically from China, Vietnam and other countries which do not recognize american copyright laws for the most part, its doesn't jive.
3.) Improved flight characteristics over the original design or caused by "scaling down": doubtful. Reducing the fuse area near the tail is actually going to be more of an issue due to the forces caused by flight on said tail surfaces.
4.) ease of assembly: see number 1.