In my first airline after leaving the military every captain was required to write a report on the first offers performance on every flight. If these were consistently above average, and you passed two consecutive base checks above average, and you maintained this standard, you would go into the pool for promotion to command. Seniority was only used for redundancy (LIFO). I was promoted from 197 on the first officers seniority list. This method ensured that FO's performed to their best ability all the time instead of just warming the right seat until their turn came round. It also reduced the failure rate to almost zero thereby saving the company a fortune in wasted training time.