PSI has been a pain in the ass from the day it was released. I can happily ignore it, but my customers don’t.
I have clients that made a big deal about PSI and did all sorts of things to raise their old scores. Then the system changed and they went from scores in the 90s to scores in the 30s.
The new system tends to brutally punish things like ads, even Google's own AdSense. Slow servers, bloated HTML/JS/CSS, all those things that make browsing painful get penalized in a much more fair way than before.
But, the sudden move from basing ranks off median vs to the 90th percentile, needs to be considered. (Or at least some function on outliers should be applied perhaps weighted by pageHits).
From my initial querying of CRuX and using the tool directly — it tends to punish highly trafficked sites, making it seem like they are "slower"...when they are often highly optimized.
My advice. If your site it's over 70 you're probably good.