Headers vs 340 manifolds

I have seen dyno tests of headers, cutouts, and mufflers, where a completely mismatched garbage system was used as a baseline, in order to make the parts they are promoting/selling look as good as possible. GIGO testing.
(Example: EM trying to make cutouts look good. 800hp bbc, that needs 3 1/2 pipes with straight thru mufflers, gets tested with 2 1/2 exhaust and triple pass turbos of questionable quality. OF COURSE, the cutouts look good! Put the right system on it, the cutouts won't do squat!)