It would take the US investing in tank production and design a few year's earlier. Then using those tanks in combat to receive real data. Just like the Germans, British, and Russians.
The M4X improvement program started in May, 1942
First M4A1 built were in February, 1942
First combat was with Lend Leased M4A1 in October, 1942
Early design was this, from
ASF, Army Service Forces
Note M6 Tank suspension components
Before things shifted to the T20 series
Now All ASF requests had to go thru AGF, Army Ground Forces, headed by McNair.
Ordnance wanted the T20 series.
McNair didn't want either.
He wanted three things
TDs
Towed AT Guns.
As many M4s as could be built
General Barnes, the leading supporter of the T20 series, wanted all new medium tanks to have the 90mm in March, 1943.
He was overruled by McNair. Do note that Barnes meant 90mm what would be the T25 and T26, not to upgrade existing M4s or for the T23.
He was very against that, thinking it would be 'unbalanced'.
McNair really didn't want the 90mm even in what would be the M36, but wanting it towed, instead.
Now how fast could a new design be done?
The M18 Hellcat, went from paper to production, and had little parts commonality in any other AFV, in just over a year.
That project, however, had McNair's blessing, that brought with it AA1 production priority.
The T20 was much lower priority