Also a shame because resources could have gone into creating better allied tanks earlier.
Well, the thing is, at this point nobody knew what a "better tank" looked like. All of this shotgunning of ideas and prototypes, etc. on both sides, was in an attempt to home in on what, actually, was a better tank. Prototyping was the tool used to establish if a concept had merit. Really most of these prototypes were being used to inform what the requirements _should_ be for new vehicles as the groups involved, especially on the US side who were both new to the war and very new to having access to the amount of money needed to manage a lot of new armoured vehicle design.
On the American side, while this was being tried, the Sherman was going through a number of experimental concepts to improve the suspension and increase the hitting power, and, at the same time, the T20/T23/T26 program was evolving a new medium tank that was definitely better, the M26.
The US, and to a lesser extent the other fighting powers, were all going though phases of creation that required, in the end, that a large number of ideas be tried before concepts could home in on what actually would work better.
The Germans and Brits were doing this on the battlefield and getting real life feedback. The Yanks were not in much combat before 1943 so the results of combat feedback were limited. This was not helped by a significant amount of Anglophobia and parochialism on the part of the US teams. They believed, without any experience, that they knew better. In lots of areas, not just tank design. In some cases they were right and in many cases they were wrong and paid a price in men and materiel.
Paul