I'm pretty sure that the Americans were making the Shermans, which made the Grant "substitute standard". Of course, that label doesn't mean anything; the Thompson was labeled "substitute standard" although the standard SMG (M3 Grease Gun) was most definitely inferior.

The Grant and Lee worked very well in North Africa. The 75mm side turret could kill any Axis tank there from the front, and the 37mm wasn't that obsolete back then, either. And the British, of course, were happy to get something that actually allowed them to take out German tanks (two-pounder guns...ugh). Admittedly, it suffered from the long-barreled 75mm Panzer-IVs, but there weren't many of those things out there.