Product execution mock interview: YouTube Shorts (w/ Microsoft PM)

I wonder if the North Star Metric should always be ONE and only one, to track the success of the product. While the prioritisation of Product Health metrics (Growth vs Engagement for example) should be reprioritised based on the stage of the product

He predecided to evaluate yt shorts at the Global level?? Without even asking from the interviewer

Growth is great but he should have picked Engagement for the North Star. Growth is nothing if users are not staying on the platform or engaging.

Is it better to choose the correct bucket of metric first (growth/adoption) and then dive into the different intermediary metrics for that bucket or is it better to do what he did where he listed all the different buckets and then list intermediary metrics for each bucket and then finally narrow down and choose the right one?

I feel like doing the former saves time and narrows down the scope quicker. Why go through a bunch of leading metrics for engagement and monetization when you know that adoption is the one that you should focus on based on your current product's state?