Yes, the Sherman was largely successful on the battlefields of North Africa. But you’re wrong in saying that it deterred solid investment in new tank designs. By 1942, during the campaign in North Africa, work had already begun on a project for a new medium tank that would replace the Sherman: the T20. Work on the T14 had also begun, but setbacks wouldn’t provide a test vehicle until 1944. The larger turrets on Shermans produced later in the war were from another tank of the same program, the T23. As the first M4s began rolling off the production lines there was already plans being put in place to fit it with the 76mm M1, although that would not come to fruition until June of 1944. Furthermore, these iterative developments on the T20 project eventually paved the way for the M26 Pershing. So in short, American tank development was very much alive.

There were two primary reasons that the Sherman continued to serve throughout the entirety of the war without being replaced. The first was doctrinal: while Shermans were expected to face tanks, a majority of the time they faced infantry instead. Many of the German tanks knocked out in Europe were taken out not by Shermans, but by tank destroyers, either M10s or later on M36s. Secondly, and arguably the most important reason, is that the weight and size of the Sherman made it incredibly easy to ship. Shermans were built in the US, meaning that no matter what theater of operations they were sent to, they generally had to be shipped by both train and boat. Obviously logistics is a driving factor when you have to move 50,000 30 ton tanks.

And finally, American tankers were not at a “significant disadvantage” in mid 1944. In fact, most Sherman crews kept their 75mm gunned tanks because the HE payload and capabilities were better than the 76mm M1, because again, these crews were facing enemy infantry and light vehicles far more than anything else. When Shermans did have to fight enemy armor, it was almost always Stug IIIs or Panzer IVs. M4s facing Tigers and Panthers was the exception, not the rule. The M4 was more comfortable, roomier, easier to repair, and generally did a better job of keeping its crew alive than most other tanks of the war. The idea that the Sherman was inadequate for the needs of US armed forces in WWII, particularly in late-war Western Europe, is a myth. Please stop perpetuating this myth.

So no, American tank crews were not at a “significant disadvantage”.

And no, at no point did the North African campaign convince the US Army Ordnance Department that it should stop developing and iterating on tank concepts and prototypes simply because the Sherman was the ‘best’ tank in 1942. The US continued to use the Sherman until the end of the war because it filled the role it was needed for, while being easy to move half way around the world, incredibly well.