Your point about essential complexity is absolutely correct, but your faux mathematical analysis is totally not a legit way to analyze the complexity of something or determine test coverage. I feel like as programmers we should be comfortable making sensible statements without making up shady pseudo-math to sound convincing.
It's abundantly clear that I'm not making a precise computation here. My argument is that tests don't scale linearly with the number of features because interactions between features need to be tested as well.
