Most of us going “Luke really wouldn’t do that!” just plays into the whole theme of Luke as a legend and Luke as just a man. The idea that the legends had a clear hero’s journey in which Luke became and continued to become better is just that: a pretty story. As much as Luke learned, and as good of a person he is at his core, he’s still fallible. No one of us can say we hadn’t repeated our mistakes, or had moments we thought we were better than. There’s nothing more human than having one fleeting moment come and pass, changing everything, and you can never take it back. Luke had the galaxy on his shoulders, and he felt he failed it.

“I can’t be what she needs me to be!”

That theme connects to Poe/Finn’s plot too; their efforts to forge their own heroic legends, with the Dreadnought, with their “disable the tracker” plan, all ended up being for nothing or at a heavy cost in the end. Instead of looking back to destroy or run from what you hate, for example your past or your regrets (in the case of Luke and Kylo) or in fighting your enemy (Poe), you live with it, and move on to protect what you have left - the future.

Idk, the more I think about it, the more I like it.