A single 20mm round cannot act like a bigger artillery shell but multiple 20mm rounds?
Here is where Mr. Bender confuses the effectiveness of modern 20mm guns (or post war guns) with the 20mm KwK. The post war German gun could fire about 30 shells in two seconds. Not only machine gun like even if the shells do not explode but shells hitting the ground, structures, large trees/branches and parts of the gun itself (trail legs, etc) can explode. The WW II German
TANK guns fired at about 4.5 and 8 rounds a second but had that 10 round magazine. After 2 seconds everybody in the target area will have gone to ground and be much harder to hit with either mg bullets or 20mm shells. A 20mm Flakvierling can fire 80 rounds in 2 1/2 seconds which explains a large part of it's effectiveness. Cutting the number of rounds fired to 1/8th and using AP instead of HE and the effectiveness becomes ?????
20mm HE shells
may work against the shield on an AT gun and blow a hole in it. 20mm AP rounds will go through it. However a 2pr projectile going though the shield turns 4 times as much metal from the shield into splinters as a 20mm projectile. Getting hits on the shield is a real problem as the AT Guns are so much smaller than tanks. Getting hits on the barrel or recoil system is pretty much a matter of luck.
Trying to hit barrel/recoil cylinder at 600-900 meters?
Both guns (20mm Kwk and 2pdr) are pretty ineffective against dug in or positioned AT guns, or soft targets in general.
Again, perhaps the armored cars with their high angle mounts had HE ammo that could be used against ground targets too but it doesn't seem like the MK II tanks had it.
we could get into the shoulda/woulda game (British screwed themselves many times over with their obsession with cheap ammo) But
as used both guns had similar limitations in target effectiveness. Germans masked it much better because they seldom used MK II tanks
alone in units larger than platoons after the very early part of the war so there were usually some other tanks in the company that could fire HE, unlike the British who had too few HE firing tanks for far too long.