I used to describe project in three sections:
Not every project is straight line. Some projects have lot of ambiguities and need lot of discussion to clear those ambiguities, certain features where we spend are de prioritized/removed, process challenges, changing direction/vision. How to explain all these as a story to express the complexity of the project by showing the challenges faced?
I'm not familiar with the structure of Amazon promo documents (feel free to enlighten me), but I did leave a lot of my in-depth thoughts about the SDE 2 to SDE 3 promotion here.
It's very true that projects aren't a straight line - In fact, if you want to become a senior engineer at a FAANG company, the projects you take on should not manifest as a straight line. A key trait of a strong senior engineer is being able to handle ambiguity and thrash.
In terms of how to capture that, I think your 3-part format works just fine. At its core, every project is effectively a series of problem -> action -> impact.
For example, let's say that your project hit a snag as you realized some dependency didn't work:
For performance review at Meta, this was naturally split up as SWE performance was organized by axes:
Impact was more about the "what", and Direction/People in particular were more about the "how". So when I captured these stories in performance review, problem/action was mainly in the Direction/People sections and impact was in, well, Impact.
I think Alex point on capturing the challenged faced as your three section works, it is similar to what I used in my L6 promo.
The harder part in addition to documentation is to find supporter/feedback provider at L6+ that would support that the same view as you that what you encountered was complex and challenging.
What tend to block L6 promotion is showing that you influenced scope outside of your immediate team. Once you are able to express that and show that you meet x% of criteria in the L5-L6 role guideline, you are good to go.
Since they removed the TPA requirement, it is theoretically easier to move to L6 now.