Is the stamina feature actually useful?

Stamina seems to be off greatly, or maybe I'm interpreting Stamina incorrectly.  I did a Fondo that lasted 6.5 hours.  I was completely empty according to Stamina after the 1st climb, recovered slightly, then went empty again after the 2nd climb until the end of fondo. I completed all 4 segments in good times.  There were some sprints as well that I participated in so having no stamina can not be correct, can it???

For my shorter, less intense rides, Stamina felt accurate.  The last two rides I have gone all out and the Stamina does not seem to be correct.

I tend to the view that in races, you just have to do what you can to stay with the pack. If you drop off the back because you are "conserving matches", you are probably out of contention for the win anyway. I think the psychological effect of seeing "Low Stamina" is going to be more of a negative in terms of winning races (mainly because you can't see that everyone else has "Low Stamina" as well. 

But I can see the feature being more useful in a challenging Fondo situation, where easing off before gassing yourself may well result in a faster finishing time (and a more enjoyable day) than going hard and blowing up in the last 1/3 of the ride..

Presumably using recent power duration curve information?

I’m always conscious of potentially enormous data being stuffed in my account - I’m hoping even if there isn’t the sense check to disregard such spikes, that after the passing of a few weeks/months they will become irrelevant?