It's comparing a guy with six fights at heavyweight against another who fought most of his career at the weight. Byrd obviously has more names on his record; it would defy logic for him not to. In terms of quality of wins, offset against losses, it's clear cut that Uysk was the greater heavyweight. Byrd has the two one-sided losses against Wlad, as well as the Ibeabuchi blowout to factor in. Byrd was never the recognised #1 in the division at any point; there may be an argument that he was the best ranked heavy between Vitali retiring and Wlad beating him, but the division was in a state of flux until the Klitschko monopoly/duopoly was established. Usyk has beaten 2 of the 3 top heavyweights of the post-Wlad era, and has effectively unified the division. The Dubois win may also take on increasing significance with time. Like any active fighter the wheels can come off and things end up looking different, but at this point it's a pretty tidy resume at heavyweight.