Seniority is the only way to go. How do you qualify who is a better pilot. Having a rating system like Qantas is very subjective, you can fly exactly the same with two different instructors and get rated very differently.
If you have achieved a suitable standard for command, and you are the next in line then you should get the job. Not someone who is deemed to be older, more experienced or a better pilot.
Seniority is transparent, you can see where you stand in the system. The alternative is not, where your company can hire who they like. Personal likes and dislikes come into play, your ability to do a job rates less than if the boss likes you !
"Older and more experienced pilots" have had their chance and through no fault of their own are now in the job market again. Most of them, like myself are happy just to be in aviation. The experience thay have is not lost, it is still on the flight deck it is just that a different person is in command. The new captain will utilise that experience and they operate effectively as a team.