Because these rheostats are prone to failure even w/o that added stress and often do. You would just be forcing it to happen sooner due to the extra load stress on it. IIRC, they are rated @ 2w and should be 10w.
Thank you Rob and everyone for your responses. For the question about the antenna and the coax. I'm using a 4ft Firestick and RG-8X. The 80 amp is enough, I run a 667V at full power with no problems so I'm certain it can handle the 350HDV.