>>42776408100 base attack is workable, especially considering the most common spreads have it running Adamant or Brave. Moreover I did say 'or some Ghost-type equivalent.' if we're talking about ideal improvement.
As for mentioning Rotom, it is brought up for the same reason Stength Sap has been. A lot of other Ghost types have it, and befit from it. When disusing how to improve a mon, one typically either proposes new moves, abilities, and/or stat changes. These are typically formulated using other mons as references points, hence the references.
Do you disagree the Dusknoir is in need of improvement, or that it even should be?