There are always "below standard" pilots who manage to slip through the cracks. However I truly believe our industry does a far better job of catching them than many other professional industries.
Medicine, for example, is having a difficult time (though it is at least trying on several fronts) catching up to aviation in this respect. That's specialist-doctor-in-the-family knowledge, BTW.
Check & training captains usually have a vested interest in making sure that someone makes the appropriate grade, and that remains the same today. The last thing a training captain wants is to be facing the Coroner, the bulldog lawyer, and the ACA journo kicking his door down asking him why he passed a sub-standard pilot on his last check ride.