Is there a bit of a "path not taken" here?
Walter Christie really threw a monkey wrench into the planned 250 purchase of the M1 above, for his very fast, and no real combat ability, the M1928 with 40mph speed on tracks, vs 25 for the M1, and a fake gun in the nose, and far less armor.
Contract for the M1 was cancelled, and returned to T1 designation. Christie got a contract for a few demonstrators, that would have a turret for later testing
Then the Depression. and spending for tanks was cut.
So Harry Knox went back to the drawing board, and did the next series of Tanks that would eventually result in double pin Rubber Block track, Vertical Volute suspension and front drive Cletrac transaxle that the US used all thru WWII
So ok, Walter get hit by a bus and is out of the tank business for awhile, and no M1928, US gets say a hundred 20 ton M1 Medium tanks before military spending gets cut during the Depression, that Congress also cut funding on a combined force research on mixing Tanks, Arty and Infantry
These M1 Tanks were in no ways perfect, and had many obsolete feature, but aborts much of the fast, light tankette desire in the Army.
But the Army would have enough tanks of the same type to really use them on maneuvers, rather than handfuls of prototypes. Then Lt. Colonel Chaffee and Major George Patton, would be able to work on armor doctrine
Knox would continue his developments to make tanks more reliable, so you would get his features on later updated M1A1 M1A2, and so on.