Infantries are ineffective if you don’t know how to even field them properly. Say you hide the IFVs and the MBTs far away in cover, deploy AT infantry with anti-material rifles, LAWs and ATGMs. So, when the Legion comes marching in predictably like they always do, the AT infantries move in and blast at them with missiles, rockets and armor piercing bullets. While tanks and IFVs pick them off with their main guns and missiles. In the end the infantry kills whatever ignores them to beeline the tanks, or the AFV's kill whatever gets bogged down trying to kill the infantry. More or less NATO will use this tactic against massed heavy armor and artillery assault from the Warsaw Pact.