Many of those were good airframes,and some actually entered service. I think the mb5 was highly regarded, it was just unnecessary because the war was ending. The Windsor was reportedly good, but with mass production of the Lancaster underway it was unnecessary. Spiteful was good, and entered service. The only problem with it was the handling wasnt as good as the spitfires wing at high mach numbers. Its wings also went on to inspire a series of supermarine jet fighters like the Attacker.
Can anyone show comparable examples of the extended development of aircraft wtypes that lead nowhere, like the Arado 240 or Ta154 or Ju288? They actually built 22 ju288s, found it was no good, and cancelled it. It only took the 2 years to figure it out.
Windsor versus Ju 288? Both had terrible undercarriage designs. The Windsor was a good basic design, but given the numbers of Lancaster and the decision to go with the Lincoln postwar, it had no place postwar, especially given the cost of its complicated construction in order to get a pressurized cabin. So Britain had the luxury of two aircraft that were easier to build to fit the role...and the engines to mount on them, partly courtesy of Packard. The Germans had nothing like that and so were always desperate to get a workable bomber aircraft that was better than what they were stuck with, but were stymied partly because they were forced to deal with the same small circle of producers of inadequate engine designs. That they built 22 and put some in service is a measure of their desperation, not of their inability to think rationally. Similar stories for the Ar 240 and Ta 154...the Ar 240 was cutting edge design, but suffered from, again, poor engines...and being a bit too cutting edge. There the promise of performance was so great that Arado stretched out the development after cancellation.
Anyway, as was already pointed out, everyone designed dogs, built dog prototypes, and even manufactured dogs. Prototypes were the only was to test things then and sometimes there was a need for something that was at least better than nothing, like the P-43. It simply wasn't unique to the Germans...but they had a much smaller industrial and development base to work from, so their dogs tend to stand out even more.