If true, then, as an advisor, your opinion would be useless.

 I agree.  I would never recommend using me as an advisor on US policy specific to the POTUS.



"Biden’s health is absolutely a factor in his policy because you have no idea whose policy it actually is. Is it Biden’s or the desires of someone working for him who is able to manipulate the policies he proposes?"

 I feel that way about all POTUS.  Do I think Trump actually came up with any of the policies implemented during his administration?  No.  He came up with building a physical wall across the entirety of the border, but there would be no feasible way to actually implement that in policy.  I figure every POTUS uses a combination of resources to promote action, some more direct than others.

 
Politics is not math. It involves countless variables and what the policies say on paper is just one.

 I agree.  I still think arguing about what POTUS is more criminal, or more demented makes little sense.  I would use actual US law, and 12 or more medical assessments for each candidate to make those determinations.  

 If Trump was a serial killer I could still assess the policies enacted over his career, if Biden were dead and his ghost took office, I could still assess what policies he enacted over his career.