Thats an understandable concern. I can see where you're coming from. I don't know if I have any thoughts that will be helpful to you, but I have considered this before. There is very little we know, or that has been revealed about the pre-mortal life. It is difficult to make too many assumptions. But we do know that we exercised agency in pre-mortality. We do know that God did see those that were noble and less noble. It is hard to say how, when, or why Christ was the way He was. It's probably not best to assume that God decided to make His firstborn perfect, but not the rest.... I feel it is still sound to believe that Christ was the way He was because of His own agency.
You're obviously familiar with the scripture that "many are called, but few are chosen." I would assume it would be the same with Christ, as it is with any of us who are given great callings. God knows our potential, and has desires for us to live up to them, we are therefore called, but in order to be chosen we must be faithful to that calling. Certainly this is the case with Christ. Christ is not, and was not perfect simply because God made Him in a way that He could not fail, but because He fully lived up to that calling. We could probably compare this to those who receive their calling and election made sure. Perhaps Christ "made His calling and election sure" in pre-mortality, had proven Himself so surely that even before entering mortality He had obtained the status of a god before He ever came to earth. The same might be said for the Holy Ghost Who has the title of a god.
The question then becomes less whether Christ was created as a robot that could not vary from what God had created Him to do, but rather goes back to the very nature of godhood. We could likewise ask if God the Father is a robot because He does not/will not change or do anything wrong. It is not because He was forced, but rather because He exercised His agency to a point where He will not because it is now against the nature He has chosen for Himself. Certainly this was the case with Christ. Christ could have chosen at any point to shirk His duty, and calling, but He chose not to because His nature had already become the same nature as His Father.
We simply do not know all that happened in pre-mortality. We have no idea if there was agency exercised by intelligences before becoming spiritually begotten by the Father. For all we know Christ as an intelligence progressed to a point where God was sure of His success and therefore chose Him to be the First-Born? Hard to say. Basically I feel like I'm rambling, and probably not being that helpful, but I guess the bottom line for me is that the knowledge we have on the subject is too limited to understand how it all worked out, but I do believe it is important to know that God the Father, His Son Jesus Christ, and the Holy Ghost are gods, and that they obtained such a position by exercising agency, not because they were "made" not to fail. It is ultimately the same for us. We are created in God's image with the potential to be the same. But we must exercise our agency. Just because some have already achieved that potential does not mean they are robots, or that they were unfairly "given" certain qualifications. Perhaps some day in the eternities when we have proven our faithfulness, and obtain the nature of god, others might wonder if we are robots, if we were created not to fail.......
Sorry so longwinded. Hope that something I wrote might trigger some thoughts that might be helpful. Good luck :)