Bronco is able to bring all different types of personalities together. he doesn't let them fracture. they follow him to the ends of the earth. He develops chemistry and unity that show up on the field.
Howell seems capable from an Xs and Os and play calling,e tc. standpoint but he seems to lack the ability to bring the whole defense together to work as one out there on the field. the communication isn't there. the playing together isn't there.
I think he has it all except for his ability to bring the whole team together. Bronco has done is year in and year out. I don't think Howell can replicate that. that is what is missing and i don't think you can teach that.
but that is just my opinion as an outsider looking in.