Your distance scales are in multiples of $$5 \times 10^{-6}$$ light years. That's around 50 million kilometres, which is half the distance to the Sun. Gravity most certainly is not constant over such distances.
If you're right then you shouldn't be needing to make simplifications and assumptions, you should be able to obtain the motion of projectiles by solving the full, non-simplified equations of motion. Newtonian physics makes it easy, $$F = m\ddot{r} = \frac{GMm}{r^{2}}$$. For relativity you solve the geodesic equation for the Schwarzchild metric. If you're right then you should be right for the full theories and it means you can exclude the possibility you're making assumptions about GR to SR or constant gravity which may turn out to be wrong.
I'll again comment that the effect of projectiles under gravitational forces and their accelerations are well tested via Gravity Probe A, Gravity Probe B and the GPS network. GR has correctly predicted the outcomes in all of them, which are sufficiently sensitive to detect the kind of errors you're claiming. You can't hide behind "Well no one has done a high velocity experiment", because the same deviations would appear in low velocity experiments provided you're doing sensitive enough experiments and Gravity Probe B and the GPS network are.
If you claim the mainstream has gotten it wrong then you need to obtain the data from those experiments, derive the GR predictions, demonstrate there's a disagreement with the results and then demonstrate your idea doesn't have said disagreement. Presently all you've demonstrated is you make assumptions which aren't valid and then blame relativity.
If you're right then you shouldn't be needing to make simplifications and assumptions, you should be able to obtain the motion of projectiles by solving the full, non-simplified equations of motion. Newtonian physics makes it easy, $$F = m\ddot{r} = \frac{GMm}{r^{2}}$$. For relativity you solve the geodesic equation for the Schwarzchild metric. If you're right then you should be right for the full theories and it means you can exclude the possibility you're making assumptions about GR to SR or constant gravity which may turn out to be wrong.
I'll again comment that the effect of projectiles under gravitational forces and their accelerations are well tested via Gravity Probe A, Gravity Probe B and the GPS network. GR has correctly predicted the outcomes in all of them, which are sufficiently sensitive to detect the kind of errors you're claiming. You can't hide behind "Well no one has done a high velocity experiment", because the same deviations would appear in low velocity experiments provided you're doing sensitive enough experiments and Gravity Probe B and the GPS network are.
If you claim the mainstream has gotten it wrong then you need to obtain the data from those experiments, derive the GR predictions, demonstrate there's a disagreement with the results and then demonstrate your idea doesn't have said disagreement. Presently all you've demonstrated is you make assumptions which aren't valid and then blame relativity.