We Metroid fans suspend disbelief when we have yet another Ridley fight after killing him in 3 previous games, so I don't think the series itself would suffer from spinoffs done well, even if they can't easily fit into the timeline cleanly.
I honestly don't really like the idea of bringing back Ridley another fucking time.
It's part of why I wasn't that much satisfied by the remake of Samus return.
I am not sure if long running series like Metroid should get a serious continuity/timeline unless the plot and worldbuilding themselves are solid enough, though I support the idea that characters shouldn't be constantly recycled times and times again.
Or worse, making Samus using a outfit.
I don't really hate the idea of samus changing outfits, considering her armor having upgrades across all games where it changes shape and colour, it could be fine if you need to find and swap to different outfits, maybe even have a story/gameplay driven implementation for changing outfit, rather than purely aestethic.
Let's put it this way: Samus has to navigate a section of the map that is at extremely low temprature that requires her armor, the area next to it is some kind of vault with an EMP field around that would disable her suit, so she needs to leave it behind while entering and collecting the upgrade/key she needs but, after leaving the place, her armor is gone and the only way to restore it is located outside the ice, so the player has to find a different way to return samus to her armor, involving either a secret path, going into the low-temprature area or a bossfight.
Ever since Super Metroid, the player has always been able to de-activate specific upgrades, especially with some becoming exclusive to others, so this is kind of fine by me, but it depends mainly on context and how its used; if its poorly implemented because muh BOTW, of course I'd hate it.