RE: arrow trajectory?
One last word, gravity NEVER changes:
Ask any physisist to read your quote:
" That third factor, gravity, changes. Because you're shooting at a downward angle, the arrow isn't flying horizontal to the ground which lessens the gravitational pull. Just like if you threw a baseball down a hill versus across a field. Throwing it horizontally across the field is going to be harder because there's more gravitational pull to overcome, thus you can't throw it as far as down a hill."
I am sure he or she would find many errors with your logic.
If you throw a baseball off a cliff, it will go the same forward distance as if you threw it on level ground.
Gravity stops the ball at the same distance.