All enlargers with lenses have light falloff, unless you have a density filter/diffuser made especially for a particular magnification ratio and lens and aperture.
Exposing a film under the enlarger is a different test. That is a test of enlarger light evenness.
Graph shows composite results from 135 and 150mm Schneider Componon-S. The picture is a piece of film exposed under an enlarger and processed to a high gamma to accentuate unevenness.