Yeah I'll stick my head up on this. Sure for some things seniority probably should be the decider (eg base transfers). However, I firmly believe that command upgrade opportunity should have a merit component. I see no reason to give someone a "go" if all their reports suggest they will not pass or are slack or have a bad attitude
Seniority does not guarantee a 'go'.
You are first assesed as being up to having a 'go'.Based on all your results from your career sims and route checks. If you are borderline you must be put through a series of sims to asses you further.
Only then are you allowed to have a 'go'.If not you wait another cycle until your marks improve.
So it is merit based, after a fashion.