(2)Obvious Mistake!

"(2) Power doesn't directly determine a car's acceleration.
...
Or, m * V * A = P(t), where A is acceleration. Now you see it plainly: As the vehicle’s speed increases, the same amount of power generates less and less acceleration!"
You are definitely right, "the same amount of power generates less and less acceleration". That's why engine generates more power as RPM (or V) increases! According to your "no gear changing" model, and that's why an engine has peak power at lower rpm will quickly run out of breath while ones continuously increase power outpu up to a higher rpm accelarate better.

Do I need to say more?