By the time a site is slow, the decisions that made it slow are months old.
The heaviest things on a page are almost always chosen early: a full-bleed video, a font family with six weights, a WebGL scene that runs whether or not anyone scrolls to it. None of those are bugs. They are design decisions with a performance price tag attached.
We try to put that price on the table while the decision is still open — so the trade is deliberate rather than discovered in an audit.