Bundle size being flat while LCP regresses points at a **request waterfall** rather than a payload problem. In the app router the usual cause is an `await` sitting in a layout. Layouts render before the pages nested inside them. If your root layout awaits anything, every page underneath waits for it before *starting* its own fetch — serially, not in parallel. Check your `layout.tsx` files first, outermost in. You're looking for any `await` that isn't wrapped in a Suspense boundary.