The phrase "poor proxy" means that something or someone is not a very good substitute or representation of something else. They don't adequately stand in for or represent the intended thing. Full definition
Sensible tropospheric heat has been the traditional proxy measurement for the energy imbalance in the Earth system, but the low thermal inertia of the troposphere, the low energy storage, and the troposphere's reliance on sensible and latent heat flux from the ocean, makes's it a very poor proxy. (judithcurry.com)
But the vents, which are rich in energy sources for microbes, are poor proxies for most ocean floor sediments, where scarce nutrients could mean a lower thermal limit. (sciencemag.org)
We also drop schools located in three North Carolina Outer Banks counties with substantial water boundaries because straight - line distance is a poor proxy for actual travel time to and from these localities. (educationnext.org)