Seniority should not determine:
- The lawyer in the firm who should get the murder cases
- The corporal in the army who should be promoted to sergeant
- The doctor in the hospital who should be the head of surgery
- The member of parliament who should be a minister
- The television repairman who should be president of the company
- The engineer who should approve the design of the bridge
- The airline pilot with the best flying skills
- The airline pilot with the best people skills
- The airline pilot with the best management skills
- The airline pilot with the best experience
- The airline pilot most deserving of promotion
- The airline pilot with the best decision-making skills
- The airline pilot most pleasant to work with
- The airline pilot most able to prevent an accident
- Etc.
Considering all the unique circumstances in the airline pilot's industry (you know them already) that do not apply to most careers of skilled employees, seniority should determine which pilot is next on the list to undergo/attempt the training for promotion from second officer to first officer and from first officer to captain. If you don't agree, you already know that you are free to pursue a career in the contracted pilot industry, or to start over at another company.
If you can't tell the difference between the careers of doctors, lawyers and bankers vs. 2000-10000 airline pilots, all doing the same job, working for one company (like BA or AC or QF or AA) that will not hire foreigners (or non-EU), at least remember that one day you will be replaced by an iCadet.