Why Lighthouse 90 -> 95 is harder than 50 -> 80

Why Lighthouse 90 -> 95 is harder than 50 -> 80
Lighthouse performance score is a weighted log-normal curve, not linear. Each metric has a scoring point of diminishing returns.
— LCP weight 25%, TCP 0% (deprecated), INP not in lab score, CLS 25%, FCP 10%, Speed Index 10%, TBT 30%
— TBT (total blocking time) is the lever most people miss: it's 30% and maps to main-thread work over 50ms
— At score 90 the curve is nearly flat; shaving 200ms TBT might add 1 point
— A single 600ms long task can cap you at 78 no matter how fast LCP is
Takeaway: above 90, chase TBT — it owns 30% of the weight.