Simplistic nonsense! And even if both were flawed, the outcome of the analysis still provides a starting point for coming to a more informed decision.
Furthermore, given that the report was peer reviewed before being published, it would appear that both the methodology and assumptions were regarded as valid; hence, unless you're implying some form of underhand academic behaviour, it has credibility.
But by all means put up your criticisms of underlying assumptions and methodology used - and your proposed alternatives - and we'll be able to judge the comparative merits of both.