Bowe could beat you in more ways physically. Lewis was better at making you fight his fight. Lewis had that something in him that kept him ambitious, kept his eye on the prize. Bowe just couldn't maintain that.
Lewis was the heavier puncher and far superior on the outside. Bowe had more versatility and was a really good inside fighter for his size, but he could be lazy at times and was not great defensively. Too me, there was a very small window where Bowe would have been a significant challenge to Lewis but outside of that, Lewis was without question better. More longevity and deeper resume.