I am afraid you are not understanding the rules. Although in one respect, you are right to say that the weight doesn't matter. On Lufthansa, the rule is designed to discourage you from taking over weight baggage. Their Terms and Conditions show that for Intercontinental flights, if your free bag is over the permitted weight, the excess charge can be as much as $450 per bag, but there is a charge for a bag which is bigger and heavier than your allowance, (between 23kg and 32kg) for which the charge is $300. It makes no difference if the excess weight was 1kg or 5kg's. If both of your bags were overweight, then $600 is correct. Here is the link:
http://www.lufthansa.com/mediapool/p...flights%20(PDF)
Don't misunderstand me... the charges are excessive. However, as you agreed to them I don't think you have any realistic chance of recovering them, and I don't think any agency will help you. It is vital that bags are measured before you travel on accurage scales, because any excuse the airline have to gouge you, they will take. I totally agree with you that the only way that we can realistically change this is by re-regulation. The airlines are abusive towards passengers.