What this study is trying to point out is that this substitution doesn't capture the increase in value from switching to the new technologies. That methodology

What this study is trying to point out is that this substitution doesn't capture the increase in value from switching to the new technologies. That methodology might not capture the superiority (or inferiority) of Netflix as a value proposition. ie if there's a one-to-one substitution of spending but you're getting more for your money, that's a deflation effect that your methodology may not catch. Usually because it's hard to quantify the relative values of different related products. Light is a theoretically interesting exception that this researcher used to prove a point.