I agree with Sidi's excellent summary and want to add a bit more context to being in a formal leadership position vs. not being in a formal leadership situation.
When it comes to the Leadership dimension in your Personal Experience Interview, there is a fundamental misunderstanding of many candidates.
There is no requirement at all for your McKinsey Leadership PEI to be / have been in a formular Leadership position. This might now come as a suprise: Ideally, you don’t even have a formal leadership role in your PEI example (e.g. business unit director, department head, project lead), but initially you are acting in a group of equals.
In this scenario you can even better demonstrate how you spot opportunities (something could be going way better, if there just was effective leadership…) and act upon those opportunities to have a positive real-life impact on the overall situation.
At the same time you can also show that the team first of all accepted you taking on the leadership role, which obviously is less of an issue if you are in a hierarchically superior leadership position anyway. To earn this trust of the team is also an additional challenge making your example stronger, especially showing that the team also follows your guidance and leadership without having the supporting hierarchical power of a formal leader.
Additionally, by proactively taking on this leadership role you demonstrate that you are ready to take over additional responsibility and risk – if you had failed in this situation, it most likely would have had a negative impact on you/your career.
However, if your example is very strong otherwise and you were in an official, hierarchical leadership role, it is for sure no show-stopper for this example – obviously, there just should not be a leadership vacuum in a situation which was triggered by you in the first place.
Hope that helps - if so, please give it a thumbs-up with the green upvote button below!