Why is it senseless? You lose the same amount of heat in joules/sec, but the total heat stored in the system is higher, since there's a buffer in it with a high

Why is it senseless? You lose the same amount of heat in joules/sec, but the total heat stored in the system is higher, since there's a buffer in it with a higher volumetric heat capacity than coffee. So unless I'm missing something, it would indeed cool slower in degrees/sec, but the effect is likely very small. (Note however that the extra volume of the ball would slightly increase surface of the coffee, losing slightly more joules/sec)