The armored assault of the 40th Army and the assault of the First Mobile Group Army were utterly different.
The First Mobile Group was highly integrated and had a large number of half-track vehicles, so the infantry could keep up with the armored forces. The tank companies in the First Mobile Group also had mechanized infantry platoons, using the M3 Grant Lee tanks as infantry fighting vehicles.
The 40th Army had none of these. Especially the half-track vehicles; Ante didn't produce them, relying entirely on Federation supplies. But the supply was so limited that no one but the First Mobile Group could get many of them.
As for the Grant Lee tanks, the 40th Army didn't have a single one.
Therefore, the accompanying infantry of the 40th Army could only cling to tanks, becoming "armored cavalry."