mass and gravity are independent? really? hrmn... lets play with the equation a bit... using a constant test object of 10kg, a constant drop height of 10m, and two planets of widely divergent mass.
Mass of Planet One = Mp1 = 30,000,000,000,000,000,000,000kg
Mass of Planet One = Mp2 = 5,000,000,000,000,000,000,000kg
Mass of Test Object = Mto = 10kg
Distance of fall = d = 10m
The math suggests that mass is cardianally relevant to gravity
If you have two objects of different masses and measure the gravitational acceleration of these masses due to a third body, you will measure the same acceleration for both masses. In your example, the acceleration of planets 1 and 2 due to the 10 kg test mass will indeed be the same (and immeasurably small). Don't forget that gravity is a two-way attraction. The 10 kg mass exerts the same force on the planet as the planet does on the 10 kg mass. In your example, the force exerted by the 10 kg mass on planet one is six times greater than the force exerted by the test mass on planet two. The mass of planet one is also six times greater than the mass of planet two. If you calculate the acceleration of each planet, you will find that for planet two, it's F/m, where F is the force exerted on planet one by the test mass and m is the mass of planet two. For planet one, this acceleration is then 6F/6m = F/m. Physically speaking, this is exactly the same situation as the one in which there are two test masses being attracted by the same planet. In that case, the acceleration of the planet will be different depending on which test mass is under consideration, but the acceleration of the two test masses is equivalent. In your last example, it is the acceleration of the planets that is equivalent. The test mass undergoes different accelerations depending on which planet is under consideration.