I think we are confusing two seperate issues here. Seniority as it applies to bidline etc etc and who gets upgraded for command. In BA upgrades come in seniority order but you still have to pass the course. If you knew how many failures there were each year you would be reassured that the system was not just churning out new Captains sausage machine style. We even have the equivalent of an earlier posters "PFO's" those who have had at least 3 goes and still failed. If you are changing fleets to get a left seat and don't pass then you end up back on your original type/seat - something that I seen happen this year to colleagues.
In terms of all the other issues surrounding seniority - how would you organise an airline with 3200 pilots and not become corrupt?