Let’s Get Straight To The Prosecution Evidence:
So you have looked at the Mobile result for your website on Google’s Page Speed Insights tool and been horrified/alarmed/bothered by the result there e.g. Tim Cook could be angered by the above screenshot.
Now the evidence that I will present here has NOTHING WHATSOEVER to do with the giant nature of these online brands but rather the fact that these:
[a] are brands/sites that we all know
[b] have terrible results on Lighthouse/Google Page Speed Insights, and
[c] sites all load instantly on any mobile device I can find
Again, their domain authority is NOT being measured by Google Page Speed Insights but their performance on Mobile is – in a frankly ridiculous way, more on that in a moment. The tool is called Google Page Speed Insights and not Google Page Speed & Domain/Brand Authority Insights.
For example, according to this tool, the apple.com website (yes the people who invented the iPhone) takes almost EIGHT seconds to become ‘interactive’ on Mobile – it doesn’t, that’s nonsense and I’ll explain why shortly, test it for yourself on your phone:

It’s a similar story on Google’s own YouTube.com, the 2nd busiest site in the world, that loads instantly on almost any modern device, try it yourself:


So YouTube takes close to NINE seconds to be fully interactive on a mobile device? Hmmmm.
Here’s how the MULTI-BILLION dollar Netflix site does on Mobile on Lighthouse – again this is NOT a measure of Netflix’s domain authority or brand value, this tool is ONLY assessing their site speed on Mobile:

and over SIX SECONDS for the Netflix site to be ‘interactive’ on mobile?

As always, my best advice is to go and test these sites (and your own) on mobile devices that you have access to – friends, family, colleagues – and see how quickly these ‘losers’ on Lighthouse load there.
So something isn’t right here.
How On Earth Is Google Measuring This Mobile Speed?
Glad you asked because here is where things get (inexplicably) funky.
It turns out, and this information is infuriatingly NOT provided on the results page at developers.google.com/speed/pagespeed/insights/ – you have to go through a few links to find it, that Google/Lighthouse is measuring the Mobile speed of your website on this device and on this type of network:
“These exact figures are used as Lighthouse’s throttling default and represent roughly the bottom 25% of 4G connections and the top 25% of 3G connections (In Lighthouse it is sometimes called “Slow 4G” used to be labeled as “Fast 3G”). This preset is identical to the WebPageTest’s “Mobile 3G – Fast” and, due to a lower latency, slightly faster for some pages than the WebPageTest “4G” preset.”
https://github.com/GoogleChrome/lighthouse/blob/master/docs/throttling.md
and this mediocre 2016 phone:
“What device and network conditions does Lighthouse use to simulate a page load?
Currently, Lighthouse simulates a page load on a mid-tier device (Moto G4) on a mobile network.”
The Motorola G4 is a slow 2016 phone and if the user is assumed to be using 3G, it’s like blaming a computer game when a user is running it on a 486 computer.
But Terry, Aren’t There A Lot Of People Still Using 3G On Old Phones?
This depends entirely on where your target customers are and if you have researched that your main target audience IS still on 3G with older devices, then yes, these tests could help.
But in North America, this is the current breakdown:

That’s 84% of people in North America in 2020 are using 4G and 5G 12% using 3G and 4% using 2G.
In short, the likely audience of your website if targeting North America, is 4G and 5G – 84%!
And in 2021, this stats site, Statista.com, forecasts that 88% of mobile users will be on 4G and 5G with just 9% using 3G and 3% using 2G.
What Exactly Does This Mean?
It means that Google Page Speed Insights/Lighthouse is mainly judging your Mobile speed performance on the users’ antiquated hardware and network technology, not on the actual, testable, ‘seeable’ loading speed of the world’s biggest websites, which had terrible mobile scores, as you saw with some of them above: Apple, YouTube and Netflix.
Would Google therefore like us to just have an ugly, text-only website that works on this obsolete tech because that is the exact opposite of where Web functionality is going in terms of ever more complex sites, functions, expectations, and interactivity?
Does Google also want us to throw away useful page-building tools like Thrive Themes, Divi, and Elementor as these make sites heavier?
In its current form, in my opinion, this tool is largely useless and just creates a lot of unnecessary anxiety. Hopefully, Google will fix it in the future.