Abstract: The discovery of massive, high redshift galaxies with the James Webb Space Telescope (JWST) has been argued to challenge $\Lambda$CDM (cold dark matter): such systems would require extremely rare halos and baryon-to-stellar-mass conversion efficiencies unphysically approaching—or exceeding—$100\%$. If confirmed at galaxy-formation--forbidden efficiencies, these galaxies could signal new dark matter particle physics. We develop a galaxy model framework that ties the linear power spectrum to the inferred efficiencies of galaxy growth while incorporating multiple sources of uncertainties in order to test the structure formation models. The sources of error include (i) observational sample variance, (ii) asymmetric scatter induced by the steepness of the high-mass halo tail, and (iii) systematic uncertainties in stellar mass estimates. We find that the inferred star-formation efficiency is largely controlled by systematic uncertainties in the stellar mass estimates derived from spectral energy distribution modeling of JWST-detected galaxies. Because of the inherent Eddington-like bias, systematic uncertainties amplify the asymmetry of the scatter, in some cases by orders of magnitude, thereby bringing the inferred efficiencies into closer agreement with expectations from early galaxy formation models. Our framework can be used to test $\Lambda$CDM as errors are reduced and further detections are made.