Samus rarely arrives while things are happening.
The icy section of Bryyo is really cool! (Pun not intended.) It’s only there for the Screw Attack, but it’s also the conclusion lore for Bryyo. It seems we got there far too late, but also there likely wasn’t anything Samus could do about it. It’s not like it had anything to do with the Leviathan Seed. The Seed just happened to land there; the civilization was already gone.
Meanwhile, we have the Valhalla, a poorly-named ship that became the graveyard its name foretold. This place’s enemies are surprisingly dynamic, rapidly increasing in difficulty as we make our way through the rest of the game, despite the fact that this is an end-game area to begin with. It’s also totally optional and won’t give you anything required in order to get to the end of the game, but it will give you lore and resources that are probably best collected whenever you can.