My take is that USA technology was clearly behind the curve with the M-2, M-3, and M-4 medium designs. We did win the war primarily with the Sherman as our tank, but it was far from an ideal tank design, and technologically speaking was built very much with yesterday's technology. Unfortunately for the American tankers in Normandy, we chose to stick with the Sherman as THE TANK, rather than viewing it more correctly as an interim solution, similar to how its predessor the M-3 medium was viewed.
Once USA put its mind to it, we caught up quite quickly. As Tigerman correclty points out the M-26 Pershing was an excellent tank with very modern technology. The M-24 Chaffee was likewise a very modern, capable light tank. I think that had the Army not looked so favorably upon the Sherman, we could have introduced the M-26 into combat a lot earlier than early in 1945.
How all this relates to the Centurion, I'm not entirely sure. As I see it, in a lot of ways Briatin and USA kind paralleled each other. At the start of the war, we were clearly deficient in modern armor, we both improved during the war, and by the end each country was producing excellent modern AFV's.