But there a difference.
The seniority system works on the assumption that the IF (and I agree with PP, there is a big if) you pass the assesment then you are equal.....
In other words, if you had a good CP candidate and a excellent CP candidate (let's face it people have different previous experiences) they are then awarded the position not in order excellent, then good but rather senior to junior.
If the "pass" mark is set to high, candidates who may be suitable will fail and very demoralised.
If the "pass" mark is set to low, well then you end up in the situation that is mentioned by previous posters, that F/O simply wait for their time.
So I wouldn't say that it's quite that simple. still for other issues such as base bid, leave etc, it seems to work fine, especially if the system compensates for achieved bids etc.
just my 2c