Stiff hearts due to cardiac remodelling get improved CO with a reduction in HF due to incresed end-diastolic volumes as described by the Frank-Starling equation.

The simple equation for CO doesn't always hold, especially in pathological physiology. There are many exceptions in clinical medicine.

Yeah, where I went wrong in particular was in misremembering the relationship with contractility. I thought a beta blocker was a positive inotrope, not a negative one. But I also have pretty atrocious memory and recall, so I figured I was missing something, somewhere.