I just assumed that was like, a bridge rather than being part of either Saga.
A bridge to where exactly? 4 doesn't exist yet. The bridge leads nowhere. A bridge in any other series, is made AFTER, the games it's a bridge between. See, Resident Evil Revelations or Dead Space Extraction for what a bridge actually is. What you call a bridge is what Dead Space 3's terrible DLC did. And guess where that bridge to nowhere ended? Right... Don't support bridges which have yet to lead you to your destination.
It's a side game which revives Xehanort to ruin his perfect finale from 3 in order to lead to 4 and because Nomura also doesn't actually know how to do sidegames everything which happens will magically be important to the plot of the next game. Similar to how Xemnas' battle in KH1FM a fight 90% of the original games' players never even had access to, is referenced in vanilla KH2 despite the majority of players having 0 context for it even if they played Chain of Memories. Kingdom Hearts' story is just like the MCU Disney also owns. Always bringing up random bullshit from a side venture that everyone correctly avoided and now is alienated by sequels constantly forcing them to go back to understand shit. "Ahh you see, it's your fault for not understanding Dr. Doom's evil plan. If you watch the Twerking scene from the She-Hulk show it's revealed..."
Compare this to Resident Evil or Dead Space. If I play Resident Evil mainline I understand what's going on in every single game because Capcom understands what show don't tell means. I'm not 5 years old I can look at things and figure them out. I'm a big boy you know (that's btw, also why so much shonen is filled with random exposition about some guys special attack, they're made for little kids so the writing is designed for people who lack brain cells) . If I play a side game's franchise I also understand what's going on. As long as I play games in order I understand the general plot. So Resident Evil 1-3, then Code Veronica, 4, 5, 6, 7, 8 and eventually 9. Yes Grace might be the daughter of a character from Outbreak, but outside of providing fanservice to hardcore fans by referencing the game's existence I don't need to play Outbreak to understand what's going on. I play a woman who's shaky after her mother was murdered and she must return to her mother's murder location to solve some mystery. Evil bad guy infected everyone at the place, which includes Leon as well. Leon and the evil bad guy must find Grace and obtain a cure from within her blood. Dead zombies mutate like Crimson Heads from RE1 for Grace because in the trailer they reveal she has an item designed to prevent this mechanic. And even if I never played RE1 I could tell from the introduction to that being a mechanic which exists, that enemies would come back stronger and attack me if I don't use it. I understand, just from the trailer, what I'm buying. I know what I need to from the trailer, without being spoiled past what I need to see. Provided some Somalian doesn't get the game a day early and upload it all to YT again. (Fuck AWS being so easy to hack).
Kingdom Hearts 1 remains the only well written game in the series because Nomura doesn't understand that a story should be good on its own and not need 20,000 other side games, half of which don't even exist yet, to understand. That's the issue with Kingdom Hearts. Not that the side games are important. They're important in Resident Evil as well as Dead Space too. But where those series fill in lore gaps to bridge to games which are already out. Nomura bridges to nowhere. What if Chain of Memories was the last game? What if Dream Drop Distance was the last game? What if Melody of Memory remains the last game? Then those bridges lead to nowhere and forever will. Notice however, that 358/2 Days could have been the last game though and it wouldn't be so bad? That's because that's an actual bridge, it goes from Kingdom Hearts 1, which already existed, to Kingdom Hearts 2, which also already existed. The bridge actually led somewhere day 1. Viola, a proper bridge in Kingdom Hearts.