By dancing around the issue as he did (i.e., heavily prevaricating), he made himself look not only misogynistic but also disingenuous. Admitting to his mistake would not have absolved him of responsibility for mistreating his female employee, but it would have given him a chance to acknowledge his professional shortcomings.
Humans care more about lying and dishonesty than they do about anything else that people do. The abilty to trust someone, even if they can only trust that that person is a terrible person who does terrible things allows people to forgive a multitude of sins including murder and rape.
The recorded name-calling and the denials occurred decades ago, but owning up to doing wrong is always the high road to take. He shouldn't have stooped to name-calling and threatening her in the first place. He shouldn't have denied it afterward. However, Bannon did what many people do: denied wrong-doing. Why doesn't matter, especially now. What's important now is that he owns up to it and doesn't repeat such trash talk.
There i a possibility that the whole thing may have been a lie to smear Trump and his campaign. There is also a possibility that he said it in a joking manner or that things were taken out of context or a number of other things. Since details aren't clear or known i should be assumed that he is innocent. Even so he has every right to call someone a bimbo.