Every FO that is in the company today will, at some point, upgrade to left seat
No my friend, no they will not. What they WILL be able to do however is to apply for the upgrade and at that point, if accepted, will begin the process to move to the left hand seat. They will then have to pass the interview, simulator training and checking, line flying under supervision, line checks and only then will they be able to sit in the left seat.
Too many people think that the command here is a given and a right and not something that you earn through hard work and the like. With that sort of attitude, it is plain to see why there have been a number of failures at all stages of the process.