So your argument is that Joshua was mistaken, he mistakenly believed the people had a choice. All of the prophets, all of the preachers who called on people to repent, to choose God were operating under the false notion that people genuinely could choose. The prophets and the people were actors in a staged performance with scripted scenes and finale. All the while very writer of the play declares His truthfulness, but the play its self is a testimony to lies and deception. It can not be so, God does not lie nor does He deceive.
Try to take credit if you must but I believe that it was a gift from God.
Ephesians 2:8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: