You questioning a soft looking, 245lb true frosh is legitimate.
You questioning the 260lb version that beat Parris in the '21 finals, let alone the 265lb version that beat Schultzy in '22 is just plain silly. There isn't a better or more athletic heavyweight than either of those versions of Steveson, ever.
If you are talking best career, that is different - perhaps. Maybe not, though. If you are talking the best heavyweight ever, the answer for 1 and 2 are the same guy.