Thank you ater
Ground speed is what determines climb gradient; i.e. "This departure requires a climb gradient of 425 feet per mile. Those miles are ground miles, not air miles.
I would add RoC in the airmass, which normally is moving WRT to the ground.
If you have a headwind on takeoff of extreme velocity, you have a greatly reduced takeoff roll and using basic climb schedule can easily have a "true" climb angle very high. Not pitch attitude, not AoA plus pitch, but a velocity vector referenced to Mother Earth. Hell, if the headwind was strong enough you could have 30, 40 or 50 degrees of actual climb compared to the runway.
The "gradient" WRT to the ground was what I was always concerned about. How many feet to get above the ground for available runway and obstacles at the other end. On one mission at heavy weight, I had the wind shift halfway down the rwy and simply stopped getting more CAS. Too fast to abort, and skimmed over the palm trees on the edge of the max AoA once up, barely. So I know what the "gradient" is. On that ride we had about 80% of available runway "computed" for takeoff considering our weight and the "predicted" wind down the runway. Then two check speeds at various rwy markers. Not something a commercial jet would go with, but it was a wartime scenario, O.K.?