From observation, promotions are awarded to the people who are performing at the next level and deserve to be promoted.
From my experience while working here, the majority of directors and managers that have been hired/promoted seem to have come from external firms, which seemed to make a number of senior people to search for career advancement elsewhere.
Completing CA speeds up the promotion process. Promotion really depends on the openings available in the firm, and the individual team structures. Hard work always gets you recognition, which gives you opportunities.
There is more of a general pathway for the first few years to becoming a senior accountant and from that point there is more of a selective promotion process to be a part of management.
KPIs and soft skill targets and regular catch ups with staff to discuss where headed and their goals, provide feedback etc.
Promotions for the first few years are automatically granted based on CA progression rather than performance.
Experience and CA are important