Aside from the fact that our edge rusher opposite Mack has generally been bad...
I completely disagree. On the contrary, I think the reason we haven't had much of a pass rush is because the coverage hasn't been very good. Ball gets out too early against us. Anyway, Fuller is good, but I veheemently disagree that he's top 10 or that you need some kind of elite corner to make him the #2. Much like E-Jax in 2018, I think the odds are pretty good that Fuller's 2018 was also more an anomaly in his career and/or Fangio making him look good than anything.
The Bears just haven't had very good corner/secondary play in general since Fangio left.