I don't think think any of these needs an open world. They were designed the way they came out for a reason. Also I've never played a persona game and thought this could be more open world lol. Also open world as a genre has its own hurdles. One of the big ones is that they can be even more time consuming. People have jobs and persona 5 is already pretty long. It alone being open world would be insane.
Have you even played Metroid? The mainline games are the 2d games that's why other M ignored things. Metroid 1 Samus Returns, super Metroid, other M, Fusion, and dread are the only mainline entries. The entire prime series has its own timeline. And they don't need retcons. I love the way they found a way to place them with the other games but they are still side games.
This somewhat set up Null as the biggest bad. Demise came from underground. Null is trapped there. It's like a soft origin for all the demons and monsters. Kinda explains why they are always around.
