Is measuring only the LCP a strategic mistake for your SEO?

What does Google’s multi-metric approach truly mean? 

When Google talks about balancing multiple metrics, it refers to the Core Web Vitals as a whole. The Largest Contentful Paint measures only the time it takes to display the largest visible element. But a site can quickly load its main content while still being completely unusable.

This is precisely why Google introduced three complementary metrics: LCP for visual loading, First Input Delay (now replaced by INP) for interactivity, and Cumulative Layout Shift for stability. Each metric captures a different aspect of a visitor's real experience.

Why can’t a single indicator be enough? 

A site can show an excellent LCP by instantly loading a hero image but remain frozen for 5 seconds before a user can click a button. Or the opposite: a site can be perfectly interactive from the very first second, but with content loading in chunks, causing unpleasant visual jumps.

These discrepancies between metrics happen constantly in the field. An e-commerce site can aggressively optimize its LCP by preloading the main product image, but if the "Add to Cart" button remains non-clickable for 3 seconds, the experience is ruined. Google knows this—hence the statement reminding us of an often-overlooked fact.

How do these three pillars interact with each other? 

The real challenge lies in finding balance. Improving LCP by massively preloading resources can degrade INP by overloading the main thread of the browser. Reducing CLS by fixing the dimensions of all elements can paradoxically slow down initial loading if these calculations are poorly optimized.

Martin Splitt emphasizes this interdependence precisely because many sites optimize in silos. Technical teams focus on a single red flag in PageSpeed Insights, correct that issue, and inadvertently create a domino effect on other metrics. A holistic approach is essential.

• The LCP measures the speed at which the main content is displayed (target: less than 2.5 seconds)
• The INP (Interaction to Next Paint) measures responsiveness to user interactions (target: less than 200 milliseconds)
• The CLS measures visual stability to avoid accidental clicks (target: less than 0.1)
• These three metrics must be optimized simultaneously, not sequentially
• A good score on one metric never compensates for a poor score on another

Is this statement really a novelty? 

Let’s be honest: no. Google has been communicating about the Core Web Vitals since their official introduction, and the idea of balancing the three metrics is explicit in their documentation. What Martin Splitt is doing here is reminding us of a principle that too many practitioners forget in the rush to optimize.

In practice, we regularly see sites with an LCP of 1.8 seconds but a catastrophic INP of 600 milliseconds. Or the reverse: highly interactive sites with a CLS of 0.35 making navigation chaotic. The statement does not provide new technical information—it reaffirms a balanced approach that many neglect.

What nuances should be added to this ideal vision? 

In reality, not all metrics have the same weight depending on the context. Google has never publicly detailed the exact weighting of each Core Web Vital in its algorithm. We know they count, but to what degree? [To verify]—field data suggests that the impact remains moderate compared to other ranking signals.

Moreover, the perfect balance is sometimes technically impossible. A media site with embedded videos, programmatic ads, and third-party widgets will inevitably have a higher CLS than a static showcase site. Google knows this and tolerates discrepancies—but how far? This statement remains vague about acceptable compromises.

What does this insistence on balancing metrics reveal? 

It’s an indirect admission that many sites manipulate scores superficially. Optimizing only the LCP by hiding "below the fold" content or aggressively preloading an image does not improve the real experience. Google is trying to discourage these superficial optimizations.

The problem is that analysis tools (PageSpeed Insights, Lighthouse) display individual scores that naturally encourage treating each metric in isolation. Google would benefit from providing a composite score that better reflects this desired balance. In the absence of such an indicator, the statement remains partially theoretical.

What should be done concretely to balance these metrics? 

The first step is to simultaneously audit the three Core Web Vitals on a representative sample of pages. Don't just settle for the homepage—analyze product pages, categories, blog articles. Performance issues can vary drastically across templates.

Use data from the Chrome User Experience Report (CrUX) rather than relying solely on Lighthouse. Lighthouse simulates a controlled environment that does not reflect the real experience of your users. CrUX provides aggregated field data over 28 days—this is what Google uses for ranking.

What mistakes should be avoided during optimization? 

The classic mistake: massively preloading resources to improve LCP, which saturates the main thread and degrades INP. Each rel="preload" directive must be justified. If you preload more than 2-3 critical resources, you're likely creating more problems than you solve.

Another common pitfall: fixing the dimensions of all elements to reduce CLS, but forgetting to do so for ads and third-party content. The result: CLS remains catastrophic and you have unnecessarily bloated your CSS. Dynamic content must have correctly sized placeholders from the initial loading.

How can I check that my site maintains this balance over time? 

Set up continuous monitoring with Search Console and tools like DebugBear or SpeedCurve that track the evolution of Core Web Vitals in production. A code deployment, the addition of a new third-party script, or a CMS modification can instantly degrade your metrics.

Systematically test on mobile and desktop—performance can often diverge dramatically. A site may have excellent desktop scores but be in the red zone on mobile due to blocking JavaScript, unoptimized images, or poorly loaded web fonts. Google has been primarily indexing and ranking the mobile version for years.

• Audit the three Core Web Vitals simultaneously across all key page types
• Use CrUX (real) data rather than only Lighthouse (simulated)
• Limit preloads (rel="preload") to a maximum of 2-3 critical resources
• Reserve properly sized spaces for all dynamic content (ads, embeds, widgets)
• Set up continuous monitoring with alerts for degradations
• Systematically test performance separately for mobile and desktop