She has no set beginning or end. Meaning her lineage is irrelevant, and her path is not laid out for her.

Except she's shown as a perfect unending line. That's the opposite, it's showing a literal line(age) of unescapable uniformity with no escape and no external presence...

Reflections aren't paths, and her own reflection can't be about lineage. There's also no story or character reason for that to be a concern of hers or the audiences. She wants to be reunited with her family, not to be a princess.

Luke seeing his face in the helmet showed him....

That he had failed his test, was unable to let go of conflict and attachment to material concerns, and to convey that he was not ready for his final encounter. It's foreshadowing of his upcoming failure to defeat Vader, as well as artfully establishing their soon-to-be-revealed connection.

Rey is Rey, no more, no less.

The issue being that this isn't the "what you is? machine", but a specific test of maturity and 'enlightenment' that reflects on her desires while visually representing the subconscious of the character...

Rey knows she's Rey. We know she's Rey. What does learning that Rey is Rey tell us about Rey? What does Rey need to change to overcome being Rey? What will she have to do differently in order to succeed in her goal of being Rey? ...