JSM didn't get kicked out, she just got 1 season. We can argue/debate all we want but we won't get the director to change his mind. This drama really boosted JSM's popularity ( win win situation). She is already a great actress but not super popular compared other popular but not so skillful actresses from her generation. I am sure GYJ is good enough for the director to bring her back. We cannot compare these two actresses as one is new and the other is experienced.
As for Go, yes it is a step up for her but not because of she's replacing JSM but because the director's decision to cast her. GYJ is new to the industry and for the director to keep her for S2 is a great opportunity to gain new experience. If the director didn't like her she would not been able to return to reprise her role as Naksu. She didn't put gun to the director's head .
Whether she knew it or not it's not important. The director reached out to JSM to fill in for s1. Given that she and the director had good relationship she agreed to help him. She wasn't part of the plan initially but since his first choice got fired he had to look for help and saw that JSM would fit the required role.
You have remember that she signed on late to the protect and she knew that there will be 2 parts and agreed for only 1 season. No one is clowning her. She's been in the industry for a long time, she knows what's she up for.
TVN produces many great dramas for 2022. Little Women is replacing AOS s1 time slot, and it is the BOMB it's so well made and it is as great as AOS. I have no doubt that AOS s2 will be great quality and it will be as good as the 1st one.