3 months was a long time in the Gundam Shelter.
During this period, a lot of things changed with the most prominent being the massive power shift in the Red Zone. Like usual, a lot of gangs fell and others rose with a lot of new faces appearing.
In the struggle for survival to gain prominence here, powerful mystic warriors dying and fading to obscurity was not a new occurrence, neither was the appearance of new promising mystic warriors.
During this time, one of the major talking points of the massive power shift that occurred was the Berserk Gang who already grew to become a behemoth.
The Red Zone was the prime zone for beginners like Rex and his 2 companions when they just came to this shelter 4 months ago.
Most gangs in the extremely chaotic Red Zone had gang leaders who were just Intermediate mystic warriors, it was only a minority of gangs that had Advanced mystic warriors as their gang leaders.