Performance gets treated as an engineering concern that arrives after the design is signed off. By then most of the damage is already in the file.
The expensive choices are design choices
Four typefaces. A full-bleed hero video. A carousel of uncompressed photography. Each of those was decided in a design review, and each one costs seconds the developer cannot refund.
Budget it like you budget space
Decide the page weight before the layout. One display face and one body face. One hero image, preloaded and sized. Animation on transform and opacity only.
The payoff
Our last three builds shipped under one second to largest contentful paint on hand-coded themes with no page builder. Nothing was sacrificed visually — the constraints simply arrived early enough to design around.