Core Web Vitals is an engineering problem
You cannot plugin your way to a fast site. Here is what actually moves LCP, CLS and INP on real builds.
Performance plugins compress images and minify CSS. That is worth roughly a tenth of the gap between a slow site and a fast one. The rest is architectural.
Largest Contentful Paint is usually a render-blocking problem, not a file-size problem. If your hero image waits on a JavaScript bundle that waits on a font that waits on an API call, no amount of compression saves you. Serve the hero from the server, preload it, and give fonts a real fallback so text paints immediately.
Cumulative Layout Shift is almost always missing dimensions. Every image, every embed, every ad slot and every element that appears after load needs reserved space. Late-loading banners and cookie notices are the usual culprits.
Interaction to Next Paint punishes heavy main-thread work. Ship less JavaScript. Break long tasks. Move what you can to the server. A page that hydrates three hundred kilobytes of components to render static text will feel slow no matter what the file sizes say.
Measure with field data, not lab scores. A Lighthouse 98 on your laptop tells you nothing about a mid-range Android on 4G, which is who is actually visiting.
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