I can relate so much to this. When my mom died I felt pity for her because I felt that if she had been born in a different era with more mental health resources she would have been a different and happier person. I hated her for the effed up things she did but as you said, she was still a human at end of the day.
I questioned it around 8 and fully stopped believing around 10. When you behave and ask for the same gift three years in a row you start to wonder. Before that I believed that he was magic and was incredibly fast.
Years ago I didn’t want to teach my children about Santa because of the Christian connections, but then I realized why we have holidays over winter. If it makes them happy I’ll do it, but I’ll also be teaching them about all the other connections to pagan religions when they’re old enough to understand.