you are forgetting that Google has different approach towards monster inc. like Amazon, Apple, Microsoft etc. They are exempted from all such non sense core vitals. These are only for small guys like us.
I highly doubt it. As said above, page score is just a very small part of the algo. These large sites have such a huge catalogue of backlinks that it makes smaller ranking factors moot (because these are so much smaller % wise when weighted against other factors).
The reason why that smaller sites may see a bigger jump in ranking when they improve their page score when compared to other similar sized sites, is because with such a low number of backlinks these other factors become more important to the algo.
Google has probably 100's of ranking factors. People tend to concentrate on just a few of them like EAT, Page Score, Backlinks, Quality Content. We all have issues on how Google determines these (What is a good backlink and what does Google determine as spam for example). The main thing comes down to how each of these ranking factors are weighted, and then how Google determines them.
For example Google may weight the ranking factors like this:
Backlinks - 50%
Quality Content - 40%
Page Score - 2%
EAT - 2%
Rest of Ranking Factors - 6%
= 100%
So a monster site like Amazon with so many backlinks probably ranks at 50% for backlinks and maybe page score is only 0.1%. Already they are at 50.1% to that number 1 spot. Your site may have a perfect page score that equals a full 2% of the ranking but has only a couple of good backlinks which when weighted only makes up 0.5%. Your total is only 2.5% so you have a long way to go to beat Amazon to get that number 1 spot.
(This is obviously a simplified approach to looking at ranking factors and how they work)