Look I'm a firm believer that staying on Erid is Grace's happy ending, and that it's a good look at maintaining independence in situations where a disabled person has high-care needs and works very well to that end, but I also really like that it's not perfect. He's still, like. He's still eating nutrition shakes and graceburgers, he still lives in a large terrarium and he still has mobility issues specifically caused by the planet's gravity. Like most of us on Earth would look at that and assume "oh shit that's fucking awful compared to my access to fresh air and sunlight and agricultural products" but I think it does a couple things from, like, a migration standpoint:
It does not present Erid as a perfect utopia. The streets of Erid aren't paved with gold, it's not the land of milk and honey, it's just a place. That's all anywhere is, it's just a place. And I feel like for people who've never, like, had to seriously consider leaving their home country before, overcoming the assumption that moving Elsewhere will make everything better, that rent will be cheaper and health insurance will be free and there's reliable public transit and that must mean there are no problems, and confronting the fact that it's all just places and the only difference between them is how easy or difficult it is to exist as a regular person is a really important step in successfully adjusting to a new place.
It does not put Grace in the position of having to completely denounce Earth in order to appreciate his life on Erid or to be accepted there. There is a lot of pressure on refugees and other migrants coming to western countries to completely denounce their homelands in order for asylum applications to be accepted and in many cases (focusing in on Muslim migrants here) to not be labeled as a terrorist. Grace is not only allowed to miss and care about Earth but Erid joins him in that care (especially in the book, where Grace can't actually see the stars from his biodome so Erid's astronomers have been keeping an eye on Sol and Rocky tells Grace about Sol returning to full luminence on their behalf) by offering to help him return to Earth, they just have a standing offer to do that which is a huge ask for aliens whose space program is roughly the equivalent of 1960s cosmonauts in terms of experience and successful known missions
Grace is not forced to assimilate, his integration into life on Erid is allowed to happen naturally and without interference. He understands Eridian fluently even though he can't speak it and, considering his book version AAC is a gigantic pipe organ that's not mobile or present in all the meeting rooms since it's not in the one he and Rocky meet in, at least some Eridians he regularly speaks to besides Rocky are presumably able to talk to him without it. BUT he also doesn't have to participate in all of their customs. Movie Grace (and the movie's ending I believe takes place earlier than the book's, the book mentions Erid offered to refuel the Hail Mary to return to Earth and when they made that offer is when the movie ending takes place) but Movie Grace does not have his big pipe organ AAC, just the translator laptop, and is still fully capable of and allowed to teach Eridian children, using Earth classroom materials. His house is a mix of Eridian and Earth styles, Armando is in his house, and while you could make the argument that Erid just happens to have a beach on hand that looks like Durdle Door but considering the waves are machine made and we know the Don't Go Crazy Room has a video of Durdle Door I think it's entirely possible that Rocky and Adrian and the rest of biodome team purposely reconstructed Durdle Door (the script also specifies that Grace's biodome is a replica of a specific beach)
idk I just like that all this is allowed to exist in relative normalcy in a way that both mimics real migration experiences and also, as all good science fiction should, shows what could be, and yeah this is another case of Andy fucking. Logicking his way out of imperialist views on a given topic relating to human geography and it really grinds my gears that there wasn't intention to this because if there was the stuff in the story that makes this ↑ weaker could've either been either avoided or addressed head on, but I do think it's neat that the ending is presented in this way, like this really works for me in a way that "Grace is having the time of his life on Erid" and "Grace's existence on Erid is kind of horrifying" don't like
Like there's downsides, yeah, and they're pretty big and scary downsides. But that contributes to the placeness of it all, because there's upsides, too. As far as I can tell, Eridians don't use money. They don't even have a government why would they use money? So Grace doesn't have to worry about rent, or a mortgage, or taxes, or any of the other woes of capitalism as long as he's on Erid. He gets to do the thing he loves doing the most which is teach, his health and physical needs are taken care of even if the flavor is bad (but they are, notably, trying to make it taste good they're actively working on it in the book) and he doesn't have to worry about most natural disasters (I mean theoretically an earthquake could take him out but I'm pretty sure rocky had the good sense not to put grace's dome in a seismic zone).
So like, yeah, Grace is happy. He's home, he's safe, he has friends, and it's not perfect. It's not horrifying. It's just life, and I can't think of a better way to write an ending for a character that represents humanity than to have it be life on such an intrinsic level