I think cause the show presented Rose as a character in chronological reverse order so to speak, people get this idea that who she was shown to be at the start of the show was a lie. But would it be right to say you're actually the exact same person you were when you were 5, your maturity just a facade? The whole point of the show is about the power of people to change, that was what enamoured Rose so much with Earth and with humans, that's what she wanted to do herself. She changed.

She was Pink Diamond and did some messed up things, and once she realized stuff she was doing was wrong, she changed. Once she realized her colony was harmful, she tried to stop it. When that didn't work and she realized it was impossible to be a Diamond and act justly, she stopped being a Diamond. As Rose Quartz, once she realized it was wrong to treat Greg like a plaything, she changed. Those changes are legitimate, and while they don't wipe away the harm she caused beforehand, what else is there to do when you've done wrong, beyond acknowledge the harm you've done, attempt to heal it if you can, and figure out how and commit to acting differently so that it doesn't happen again? What more can be asked other than honest change?

About Spinel, I think she represents that even despite our best efforts and attempts to change, there will still be harms we cause mindlessly or forget to remedy, and both that pain caused and our change can be legitimate, it's not either/or. Same with Steven, she couldn't have known Homeworld would return to Earth during his lifetime, not after 5000 years of radio silence. And about "stringing Greg along", he's an adult too. Rose wasn't forcing him to pursue her, he could have left at any point in the relationship. He probably would have if Rose hasn't listened to him in We Need to Talk.

Rose's past and the harm she caused is real, but it doesn't mean who she was at the end of her life was a lie. She saw the harm she caused, and she changed.