What I think would be so funny to me in making Eridians and Solarians/Earthlings so different is just how fast they evolve. Microbes can multiply into several generations in a few weeks, because the replication of DNA is so common that new, more efficient genes can pop up quickly and easily. It's how Grace and Rocky bred the Taumoeba to withstand nitrogen so quickly. Especially in the case of radiation, which the taumoeba must have the incredible ability to bounce back from due to it needing to be so close to its prey. It'd have to rebuild its mutating DNA just as much as it has to reproduce, not because of some sci-fi reasoning, but because radiation breaks apart DNA and need to be repaired, which can cause genetic abnormalities, such as cancer, which is when the replication genes of your cells go haywire and begin to replicate much faster than it should, creating tumors.
Humans reproduce relatively quickly compared to Eridians. We live and die like a mayfly, with a genetic instinct to want to continue our genetics and diversity our gene pools (at least as a hypothesis for mating in social science). Stepping outside exposes us to radiation, and our bodies learned to metabolize it. Eridians, on the other hand, have all the time they need. They, comparatively, have no need to rush, and considering how long they live, evolution would likely encourage single children to be born at a time, or else the ecosystem would be overburdened. They move much slower than we do in an evolutionary perspective. While humans can pop up new gene pools willy-nilly, Eridians take time to do so, since they wouldn't be spreading new genes as quickly as we do. The time it must have taken for a human to evolve from an ape to a homo sapien is minuscule, and likely within Rocky's species' lifetime.
Additionally, Erid likely doesn't have as much intense weather or seasons. Weather and seasons erode rocks, which isn't very helpful if your exoskeleton is made of the stuff, and you can live a couple hundred years. So their temperatures likely stay pretty stable, and Erid's axis is rendered either 0 or 90 degrees tilted, relying on how Earth's measly 23 degrees is the source of all of our seasons. Erid is a crystalizing diamond in a volcano where Earth is a chem lab throwing shit into a pot to see what sticks. The funniest part is that evolution doesn't give two fucks about efficiency or optimization of the living things it affects. It occasionally tries a few things every once in a while, and it either kills or makes the next generation better, and then it dusts off its hands and says "good enough". Which means that the Eridians likely existed for longer than Solarians did, and Grace and Rocky's technologies just so happened to be so in sync (because they're soulmates) because Eridians are blind and couldn't have even conceptualized the vaccuum of space for a long time.
Eridians are seemingly so much more efficient compared to humans because A) they had the time to and B) their planet isn't God's pet project. Solarians are, above all things, scarily adaptable. Humans can seem like extremophiles to each other, simply because we've spread and evolved to withstand the conditions of the entire globe.
So the Eridians are minding their own fucking business, trying to stay alive and passively plotting another team to go investigate Tau-Ceti, because their last crew hasn't come back, and their star is still dying. And one of their MIA engineers pulls up with dying horse (which are notorious for evolving into pieces of shit that evolution said "eh, good enough" to) and threatening to nuke the planet by not coughing up the astrophage solution if they don't help this alien fish. It can't breath their air, eat their food, use their medicine, or even live on their surface, but the engineer does have the solution, and the poor thing doesn't deserve to suffer, so they try.
It's a miracle this thing is alive at all. Starvation of essential heavy metals, carbs, and nutrients to this level would have killed any healthy Eridian. Its body is cannibalizing itself and falling apart at the literal seams, but it's alive and breathing, somehow. You finally get it what it needs, and it starts to improve, so you finally cart it down to the surface. It's weak blood vessels burst from the pressure and it's little bit of strength seemingly fails it, but the engineer keeps threatening to go berserk if you let up feeding it. That it's species lived on a planet with half the gravity of yours, and it promised its body could "get used to" the gravity. The alien is touch-and-go again, but you listen to the engineer.
And it does, in fact, get better. Its rapid decline when out of 0G is reversed faster than an Eridian in a condition similar. It stays awake for longer. It's extensive injuries self-repair with care from its strange robot. It sits up and speaks and mimics basic pebble talk. It's on its feet faster than anything you've ever seen on deaths door the way it was. The engineer had been right. It gets squishier, something it calls "muscles" that help it move grow bigger, helping it support its bipedal body. It grows fat cells to store energy to be consumed during the day by the body. Its organs grow strong again. You hear how it survived damages to roughly 20% of its body getting the taumoeba from its home planet. You hear how it had no hands-on experience with space, and yet managed to adapt to 0Gs alone with the corpses of its crewmates, relying on poorly recalled memories of brief training with the other astronauts. How its species could withstand heavier and more bipolar weather patterns than Erid has mustered.
Your species could likely live on Earth relatively easy. Proper shelter, heated ammonia, and food would fit your needs and so long as you didn't step into the oxygenated air, you'd be fine. But you'd never adapt as quickly as that human the engineer brought back. All things considered, it was thriving on Erid. An Eridian in a similar situation would have cracked under double the gravity with a brittle carapace from malnutrition, and likely died. Their species was deigned for Erid and Erid only. Humans were designed to adapt their bodies to wherever it needed to live. A horse is a horse, but you can't deny that it did well evolving to run fast.
