It's the fairest system and while seniority (or the lack of it) affects your quality of life enormously when one gains a little it does not mean your simulator / line checks / conversion courses / command / upgrade training get any easier.
I don't know how it works in the Doctor / Lawyer / Accountant world but I do know they have nothing to do with being an Airline Pilot.
No matter how senior you are, if you can't cut the mustard, at the least you will
never see the left seat and at most you may be asked to leave !