Zooks are ok but saying PIAT ok is really stretching it. Also UK is weird when Sappers using Bren better than IS.
Im not really saying that zooks on RETs are OP I'm just saying how USFs don't really lose any AI power by getting more AT power. When you get Shreks on pgrens you lose half their DPS making them pretty bad vs infantry whereas USFs and UKFs don't have to put them on expensive infantry to gain some AT power. Just give them to your cheap sappers and RETs.
If we take away zooks/ piats from sappers and RETs then it force Allies to choose between more AT and less AI or more AI and no AT since it'll have to go on their mainline infantry