I Seen that video long ago and I disagree with it. You put enough dents in a header tube and if they are deep enough it sure does affect flow. The best way to avoid having to beat on headers to begin with is to buy a quality header such as Doug's or tti's.
maybe you need to go watch it again and refresh your memory. the amount and degree to which they dented those tubes up far exceeds any amount i've ever had to massage a header in order to get it to fit, and i'm sure it's the same for most others.
and what was the outcome? that's right, nearly nothing.
again, you're over here speaking like you're an authority on the matter when you don't have headers and don't even have a car.
i'll agree to the point that buying quality pieces like doug's or tti eases the install process, but as OP showed, even the cheapy summit units don't require mangling if paired with the right combo of parts.