What you're leaving out is that the legacy Bitcoin chain gets hammered with high fees and slow confirmation times when its hashpower goes down, while Bitcoin Cash just produces bigger blocks.
There are already over 100,000 unconfirmed transactions on the legacy Bitcoin chain, and ALL transactions go into the next block on Bitcoin Cash, even ZERO fee transactions. This is going to result in the price swinging far into Bitcoin Cash's direction, and making it more profitable even with a higher difficulty.
RE: Why betting on Bitcoin Cash is a really bad idea right now