Stock CQB units are not essential in wining.
All other factions have stock light AI vehicles to fight against CQC units in the early mid game. Soviets have stock flamethrowers, the M3 and Penals to ward off CQC units. OKW has Sturmpioneers and STG 44 Volks, Ostheer has stock flamethrowers and PGrens. USF has close to mid range orientated mainline infantry.
The UKF are the only ones who can consistently get overrun by CQC units (most notably on urban or other CQC orientated maps) because they have nothing in their stock arsenal to efficiently stop CQC units. The Universal Carrier can work, but doesn't on most CQC maps. The AEC doesn't deal enough AI damage.
Now since we can't magically conjure up a new AI vehicle, and since we do not want to buff Royal Engineers or the AEC for obvious reasons, they will get the Assault Officer to help defend Infantry Sections from getting overrun by CQC units.