The point is that if this system was in place, and the fixed reward was small, there would be no "ASIC boom 2". There would be no "massive investments in next gen ASIC". This is because there would be a super incentive to not have too much mining power. Not only would the difficulty increase massively, so would the block size, leading to less fees from the users. Justifying the investments in massive amounts of new mining would be quite impossible.