This is bold claim for which you have no evidence. If it is possible to progress sufficiently in a pre-mortal state that exercising agency in this life is not needed then I see no reason why anyone should be sent to earth before reaching that state. Additionally, this would imply that God specifically places these "special" spirts into those situations in which they will die young.
No, I completely reject your reasoning. This is not a God worthy of trusting. This would be saying that we should trust God loves us, but we don't really have any idea what love even is.