Presently, Sheyan was a one man party while others were in multiple people party. Therefore, even though Sheyan had placed first in terms of contribution score, his overall contribution score could not compared to the combined score of other parties. Furthermore, this historic storyline battle: Destruction of Paragon fleet (Preface), was started by contestants like Sheyan, it would similarly attract other high level contestants to participate.
Merely, those high level contestants had to likewise face higher level storyline characters; for example, Jack, Blackbeard etc. They had the same battlefield as the likes of low level contestants like Sheyan, but the nightmare realm would not arrange any form of interactions between the two groups. Once the historic battle ends, those high level contestants would be transported out of this world, and would no longer stay in this world.
