Yes, you are correct, it is an important feature, but you need to understand that ATUM was developed to help with stock management and is free of charge. Our resources are limited and we need to decide what to develop first and what is more important/requested by users.
We would like to bring COG premium add-on next year with the full capability of proper profit and loss calculations.
Regarding the stock screenshot, I am not sure why you have it in negative figures?
Can you show me a screen from the variation inventory, please?