Aiming to extract cosmological information from linear scales of the WISE×SuperCOSMOS photometric redshift catalog, we perform a characterization of the systematic effects associated with stellar content, evidencing the presence of contamination and obscuration. We create an integrated model for these effects (which together we call "usurper contamination"), devise a method to remove both of them simultaneously and show its functionality by applying it to a set of mock catalogs. When administered to WISE×SuperCOSMOS data, our method shows to improve the measurements of angular power spectra on scales llesssim15 and the extraction of cosmological parameters therefrom, even though a significant excess of power remains at these scales. When ignoring scales l<15, we still find strong indications of systematics, albeit these can be localized in the southern equatorial hemisphere. An independent analysis of the northern hemisphere at l>= 15 agrees with the ΛCDM model with parameters from the Planck satellite and gives Ωc=0.254±0.020 and Ωb<0.065 at 95% confidence limit when combined with priors on H0, As and ns.