If a hole is punched through there will be spall.
There can be spall without hole. And hall can be punched without spall at all. Blah, blah... We could argue forever.
Destruction and lethality of spalling achievable with high velocity specialized projectiles is not the same as that of, lets say, 50 cal bmg, AP or not.
Besides that, currently we don't have any tank in game which is seriously vulnerable to small caliber weapons.
And before we continue, I'd really like to see any evidence (records, etc) of WWII tank crews being disabled/killed by small caliber AT weapons on regular basis(especially trough spalling). Just didn't happen that often. At least not often enough to worry about in game modeling...