This is some super interesting analysis, @rviscomi!
The super weak FID correlation doesn’t surprise me at all—I’ve seen a very, very weak connection between Total Blocking Time and FID in sites I’ve profiled. Part of that, I’m sure, stems from the fact that FID is a pretty limited and overly optimistic metric at the moment.
The CLS correlation being low is also not too surprising given the big difference between measuring CLS in a synthetic environment (with a very limited time window) versus the CrUX measurement (until page visibility state changes).
One follow-up I think would be super interesting: how do the individual metrics as reported by LH correlate? (Ex: LH reported CLS correlation to good CLS in the wild). I’d expect a stronger correlation (since the LH score factors in a handful of different metrics, which probably dilutes the correlation a bit).