Leadership is one of the competencies that is assessed by EPSO, however, it is only required for Administrator (AD) roles but not for Assistants. Leadership does not necessarily mean a managerial skill but rather the ability to deliver results, gather a team or co-workers behind a specific goal, make sure there is no deviation from plans without prior consent and a certain level of social adaptability is also needed.
See also:
Analysis and Problem Solving, Communicating, Delivering Quality and Results, Learning and Development, Prioritising and Organising, Resilience, Working with Others