I am incredulous. Do pilots really sit in the right seat with BA for 20 years before getting a command. I simply cannot believe that anyone would do this.
Incredulous? Really?
It's not rocket science. Roughly half the pilots are FO's and roughly half are Captains. Not much comings and goings at BA so you spend half your career in the right hand seat (20 years) and half in the left hand seat (20 years). For that to change by much, you'd need to have either serious expansion (which BA has not had) or a high turnover of pilots (which BA has not had).
Simples!