How good is good?
I've been a check airman for major 121 carriers for 18 years, and I can tell you there is no practical way to grade pilots on merit or ability.
When some seniority lists are over 10,000, no one person can check them all. There would be differences in objective standards from one check airman to another, no matter how hard we'd try. Also, as good as the simulators are, it's difficult to grade the "thinking" that is so important in a command position.
How often should the "ability list" be shuffled? How often should a PIC be "checked"? If he had a bad day, should he/she be demoted for 6 months?...12 months? The training and re-training costs would be prohibitive in the best of times....and we certainly don't have those today.
Remember - each and every pilot flying the line has met the standards required by the their company, the FAA and other agencies, and those standards are tough. Not every pilot makes it. You've got to be good just to get the job. And yes....sorry to say that on occasion a pilot has to be terminated.
Anytime you take a random sample (to say nothing of a 10,000 pilot list), some will be more talented, more proficient, etc., but I'd let my grandkids fly with any of them. If I wouldn't, I'm not going to pass them.