If I put a 100 pound weight on a scale and the scale read 100 pounds and then I added a 1 pound weight and the scale read 99 pounds, I would conclude there is something wrong with the scale. I wouldn't conclude that sometimes more mass = less weight.

Adding mass to a scale ALWAYS results in more force exerted on the scale. Increasing arrow mass ALWAYS results in increased ke. In either case, if testing indicates otherwise then something is amiss.

The fact that increasing arrow mass results in increased ke may not be as intuitively obvious as the fact thatincreasing the mass of an objectresults in an increase in the force exerted on the earth, but both are equally true.