I don't think thats entirely true.
It seems that the damage value given is a baseline damage value. As in, it will never do less damage than X at Y range.
However, that can decrease depending on a number of circumstances, and that components of the tank (say, engine for example) can have catastrophic failures that result in the destruction of the tank.
You can two-shot a Panzer with a 37mm, while sometimes you need 3 75mm rounds. Does that mean the 37mm does more damage than the 75mm under the best of conditions? No, it just means that the 37mm rounds happened to hit a location on the tank where the damage done would be particularly effective.