Tank versus tank, like fighter versus fighter, was never the raison d’etre for either weapon; it developed naturally in the course of actual warfare.
Tanks were originally intended to attack stationary targets and personnel (as you wrote), and fighters were originally intended to attack bombers (which is why the USAAC/USAAF called them Pursuits, not Fighters). In fact, tanks were largely viewed as mobile artillery pieces.
Because American tanks followed outdated WWI/Interwar field artillery standards for Guns - short-barreled and low velocity guns to preserve barrel lining for very long life (much longer than the real-world life expectancy for the tank itself) - the 75 and 76.2 Tank guns were soon inadequate. As a result, the M10 and M36 Tank Destroyers became highly valued when tank warfare was necessary.
As I recall, even when they used the 76.2 - versus the 90 - they had a longer barrel for better ballistics. (That is old memory; I could be wrong.)
George Patton was a brilliant tactician, but he was mistaken in maintaining the adequacy of the M4 Sherman: It had a high profile (radial aircraft engine), narrow tread (obsolescent non-Christie), and a low-velocity gun (whether 75 or 76.2).
That is why the British did for the Sherman what they did for the Mustang: upgraded it. They gave the P-51 the Rolls Royce Merlin; they gave the M-4 the 17-Pounder (76.2).
It was called the Firefly, and it was offensively equal to the challenge of taking out Mark IV, Panther, and Tiger tanks in frontal assaults. The British used to hide a Firefly in a squadron of normal Shermans; the others baited the German tanks to engage, and the Firefly took them out.
Ahem. M18 Hellcat?
Patton was correct in the M4 Sherman’s adequacy... for everything but tank v tank combat. The M4 was excellent for antiobstacle and antipersonnel usage. And to be fair, most of the time they weren’t fighting other tanks.
“George Patton was a brilliant tactician, but he was mistaken in maintaining the adequacy of the M4 Sherman: It had a high profile (radial aircraft engine), narrow tread (obsolescent non-Christie), and a low-velocity gun (whether 75 or 76.2).”
The Sherman may have been inadequate in specific ways to their German counterparts but they had many strategic virtues, and that made the US Tank Force superior to the Axis tank force. Yes, American tankers were dismayed by their armor, but a US armored division was better than a German counterpart by 1944 and that is what wins wars.