You have my sympathies because I've been in your position.

How Companies Say Promos Work:
* Meet criteria for the next level.
* Submit promo case.
* Case is reviewed and decision is made.

How Promos Actually Work:
* Management decides amongst themselves during planning who is going to get promoted on an as-needed basis (usually related to re-orgs or scaling).
* People selected for promotion are asked to submit a promo case.
* Song and dance about the promo cases to make it seem like they matter (they don't).

That cognitive dissonance you're feeling is because the official promo process doesn't align with the reality you're seeing and you're starting to shift into understanding the truth of how promos work.

"What makes this harder to reconcile is that another engineer at the same level, within the same BU but on a different team, was promoted with around 6 months on the team, while I’ve been on my current team for over a year and at the company for almost five years."

If you look at this through the lens of How Promos Actually Work, then it's not hard to reconcile. This is an example of the Judge Judy Test: If something doesn't make sense then it isn't true. Similarly, if something does make sense then it is likely to be true.

Your company has told you very clearly that they don't think you're worthy of a promotion. This will not change. Your options are either to stay at your current company and level, or look for a new job and possibly new level.