I think if it’s required that she’s related to someone we know, Palpatine was the best choice. It’s supported by what we’d already seen, and her dark side connection at least gives her an internal struggle and retains the message of choosing your identity. I’m glad it didn’t end up being someone like Obi-Wan, because I think that would have landed with a big “So what?”
Otherwise, I think the Rey Nobody idea introduced in TLJ was a great twist, and makes force using more about worthiness and character than about bloodline. It also has that ratatouille thing of, “Not everyone can become a great cook, but a great cook can come from anywhere.” Ratatouille? anyone?
[Sigh.]
In the prequels Qui-Gon states to Shmi that they take children in the Republic to identify them for Force-sensitivity, and it is also explicitly stated that having a spouse and kids would get you expelled from the Jedi Order; from there, we can easily infer that most Jedi and Sith don’t come from special lineages.