I fail to understand why you are arguing his point. Comparatively, the developers direct purchase costs more than any other outlet they sell through. This is a measurable fact and cannot be refuted.
That being said:
OP, the problem here is that any other distributor has a network already in place. Their overhead is spread across all titles they sell, where MinMax has only this one game. That's why they can't sell it that cheap themselves, and places such as Steam can offer it to you cheaper. I understand your point, wanting to know the majority of your money went to the people who actually made the game. Keep in mind though that they should still get their revenue, no matter where you purchase it from