Yun-Seong's name is spelled as 洪潤星 in Hanja, the last character 星 literally means "star". Similar to how Hwang's name 京 literally translates as "yellow". Similar to the way the first character in Setsuka's name (雪華) means "snow".I guess it makes sense. If that is true, the REPTILE is Aeon, STONE is Rock and STAR is more likely to be Algol than Yun-Seong, honestly, I have yet to even see a good reason for STAR to even be Yun-Seong, while in Algol's case its really the best hint you can give with a name like that, so it makes much sense to be him.
Not to mention how in the official SC character popularity poll Yun-Seong scored 14th place with 295 votes while Algol only scored 33rd with 59. By the way, Hwang scored 23rd with 193 votes, so the fact they even released Hwang only makes sense if Yun-Seong was already planned all along, otherise Yun would have got priority over Hwang.