Could it be this 3vgt project was dropped as the t45 range was origanly envisiged to be launched around 1975 so rather than devolp a new cab for say 5 years production seemed less atractive than devoloping existing parts to come up with the marathon.
As for Germans been better engineers i wouldnt say thats true. But to say the allies win tge war as the brits were better engineers is ridiculous.