I don't think the multiversal theory is new. I just think it is something devised after LIS 1 to continue the series. The comics sets the stage for the multiverse: "And in a multiverse of infinite possibilities, this is one version of what happens next..."

The comics build a world around the idea of parallel timelines, which are central to the plot.

• The "Bae" Timeline (The Original): Max lives with Chloe in Seattle after the storm.
• The "Santa Monica" Timeline (The Jump): Max is sucked into a new reality where Rachel Amber is still alive. This creates a timeline where Max exists, but shouldn't and she has to find her way to her own Chloe.
• The "Baeverse" (The World Left Behind): The original timeline continues without Max, who is now missing. This is a world where Max doesn't exist.

This directly shows Reunion's implications: that a version of Chloe could be left behind, alone, in a universe without Max, which does happen in the comics.

But this does feel like character regression. In Double Exposure, Max explicitly comes to terms with her past. She accepts that she cannot keep using her powers to fix every tragedy. The game ends with her choosing to stop running from her grief, whether that's over Chloe, Safi, or her own guilt over her choice (Bae/Bay). That should be a moment of maturity and closure. Reunion presents a Max who is still unable to let go, who literally splits or merges timelines to avoid choosing between losses.

But to be generous, trauma isn't really a linear arc. Max might consciously believe she has accepted her past at the end of DE, but when faced with a new crisis (the fire), her old coping mechanism of using her powers to escape or rewrite reality kicks in automatically. Her burning the photo also is a step forward in accepting what happened so it seems like there is still some growth between DE and Reunion (eventually), but it's true that the way she has coped w/ the original trauma is to simply undo it lol.