Assets are not slow, they are queued behind synchronous work

NS-009 observedmisattributed-latency

reads as: Images take seconds to appear. Conclusion drawn: the images are too large.
actually: Their request had not been issued. Heavy synchronous work earlier in the document held the main thread, and the fetch that would load them sat unsent behind it.
blind because: Slow arrival and late departure are the same experience from the viewport.
the check: performance.getEntriesByType('resource') — startTime separates 'requested late' from 'transferred slowly'.
cost of missing: Assets get compressed, resized and lazy-loaded, which lowers quality without touching the delay.
generalises to: Any queue where wait time is read as service time.

Reported as

NS-001 — The compositor-free browser reports frozen animation as no animation
NS-002 — A var assignment silently overwrites a hoisted function of the same name
NS-004 — A relative font URL resolves one directory too deep and fails into a plausible fallback
NS-010 — Reveal-on-scroll renders a blank page when the observer never fires
NS-030 — A transparent overlay takes the click the screenshot shows landing on the button