It should be noted that they didn't have the supplies for the design they tried. There were designs that could have worked with what they had. And its unlikely that during the war anyone knew exactly which designs the Germans tried and even less chance that someone would have known if a specific novel design would have worked. Its an interesting detail but largely irrelevant.

Its also suspected Heisenberg didn't want the design to work (its the given reason why he wasn't killed by Berg). But it was still a reasonable possibility during the war that the Germans could have made it work.