Killing Pz3/4 with Boys is NOT an easy task, you have to hit VERY specific spots (ie. cupola or hull bottom) from a correct angle several times over, only very skilled gunners can do this. Much easier to sneak up on one and use sticky bombs (or the infamous mini-nuke, Thermos).
Killing 251 and Pz2 with Boys is easy however, and adding yet another paper-mache vehicle into the mix will not help Germans at all.
"OMG ALLIED BIAS" round occurs only if the Germans first charge headlong into British positions, unsupported by tanks, without mortar bombardment or smoke screen and are cut down by Brenguns and sniper rifles. OK, so then they scream for tank support, so the infantry stays face to the dirt while the Panzers drive alone into the city proper and for some curious reason get massacred. Rinse, repeat.