I experience similar differences between finger prick and Libre (and other DexCom).
I believe some people are more Libre-compatible than others.
I do not know why this is. It may be because my BG changes rapidly (especially when exercising); it may be because I move a lot which means the sensor is not stable (I have tried moving the sensor but not found anywhere I keep still for long enough); it may be my interstitial fluid is flaky; ...
With my experience, I do not think the Libre is a waste but the value is only in watching the trends.
I am able to use Libre to check my insulin dose and timing for different foods, exercise, etc. at different times of the day.
I am not able to use Libre to calculate my insulin dose or do corrections.