This is a really long way of saying “it’s not really about what the person who wrote the story says it was about!”
To me, it doesn’t work. Like you mention, a lot of what is going on in Rey’s head and in fans’ minds and speculation during TFA and TLJ was that Rey’s importance came from her family. Theory after theory was about that, when all that was really in TFA was an abandoned child, who then gets told she can find belonging in her future rather than her past.
Rey continues trying to tie it to her past though, interpreting Maz to have meant that Luke was the key to her belonging, to her family, and to her past. She goes on a similar spirit journey that Luke did, and it similarly tells her the truth she least wants to hear: that she needs to depend on herself rather than externalising it for someone else.
She wants to, similar to fans, attach her belonging to someone else’s responsibility. That her parents are people somehow meaningful to why she’s involved in all of this, that her new abilities mean she’s destined for greatness. Instead, she’s given full autonomy and independence. She’s not a lost princess, she wasn’t even wanted… but that means she can stop living in the past and fight for what’s important to her, rather than everyone else.
Making her Palpatine’s granddaughter undoes all of this, and ends up repeating the story arc of finding out despairing news. It also is a carbon copy of Luke’s arc, taking more of her autonomy and individuality away. Rather than being a product of herself, she is a product of Palpatine. Rather than having strength in the Force because of who she is, she has powers because her grandfather had powers.
Her now-loving parents are still absent, but are heroic martyrs now to give confidence to Rey, rather than her having to build confidence in herself. Her powerful grandfather brings fear, but not as much fear as being adrift.
Narratively, she went from having to create importance from within, to having external importance thrust upon her. It’s bad writing, but it’s canon now.
So, while I applaud the headcanon trying to make it make sense, sometimes we’ve got to accept that mistakes were made.