issi noho,
Generally well said, but it must be remembered that a 'seniority system' has advantages in the form of job stability. You need some kind of loyalty scheme to prevent exactly the exodus that would otherwise ensue without it. It inherently breeds company loyalty in an individual lacking in such.
It may be outdated but it works. Granted some airlines do operate without such a scheme but rarely are they in a mature state, and do so only to fast-track commands.