Don't know if you finished reading this but....uhm...Reilynn IS Reilynn. It was explained by Rachel herself around the near end of the manhwa. I skimmed most of the parts of this manhwa, but, from what I understand: Rachel tried to posses Reilynn's body when Reilynn was just born, buy Reilynn "possessed great power resistance" that it shattered a piece of Rachel's soul and separated from her before she successfully possessed Reilynn's body. However, she forgot her real purpose. That's why Reilynn (or Rachel spiritually but Reilynn physically) was a tyrant before Iris brought the time back to the current timeline of the very beginning part of the manhwa and Reilynn/Rachel took it as her chance to correct everything. That's why the "Ghost Reilynn" the our MC Reilynn keep seeing kept telling her that "I'm not Reilynn. YOU'RE Reilynn (now)". Although, I don't know if Reilynn can go back to Earth if she chose to go back. But, then again, MC Reilynn IS Reilynn.
My explanation sounds a bit confusing though, so I recommend reading the chapter where Reilynn finally met Rachel in person. It's somewhere between chapter 130-140
I don't get why other fls don't wanna go back to Earth. I mean sure you've got wealth and all that, but the technological advancement of that era is too damn slow bruh. So what if there's magic, there's no Cortis in that world. I won't be able to read murim manhwas, cultivation slops manhuas, and BLs with big titied buff bottoms. This server is indeed stressful but if you only look at the dark side, you'll sure drown in darkness. Well ig maybe cuz you've got a handsome and green flag guy as your ml then maybe you don't wanna go back at all (but James and Mairuma are not there so no).
I'm still gonna read this cuz I feel like I'm missing out (that animal shapeshifter is not the ml let's go! ε=ε=(ノ≧∇≦)ノ )