The old school on promotions had it that we promote high performers. If they got their numbers right, obviously they were ready for new levels of leadership. This tradition has not manufactured a plethora of good leaders, evidenced by the fact that over 90% of people worldwide feel they work for command and control bosses.
I would suggest that promotions happen when people have intentionally developed the kinds of knowledge, questions, personal brand and network positions that would serve well the new level. This would dramatically reduce the Peter Principle effect of promoting people to new levels of incompetence.
We would also move closer to the intention to grow organizations of good leaders.