An expression I miss in alien media is "greeting earthlings". It distinguishes that wherever the aliens came from, ours is the foreign planet to them. No matter what corner of this planet you land on, what every single human has in common is that they are an earthling.
If you don't like thinking of Clark Kent as "human", it may be better to think of him as an earthling. Or a Kryptonian-Earthling. No matter which continent he lands in, if he's been raised there since toddlerhood, he qualifies as an earthling. I'd also say if John Jones has lived here all 300 years since he fled Mars, he qualifies more than most to call himself an Martian-Earthling.
Human is often used as a synonym for sentient. It is the short term for our dominant sentient species name homosapiens. But every single alien species comics or any science fiction franchise makes up is also the dominant sentient species of their own home planets. Kryptonians are the "humans" of Krypton. Martians are the "humans" of Mars (in which two sentient species battle for dominance and it's a horrific genocide). Tamaraneans are the "humans" of Tamaran. I'm sure you remember more DC planets and aliens than I do.
I think it would be a cool world building exercise to come up with scientific names for the alien species. Names that sound nothing like their home planets, but have connotations that relay what that sentient species thought would distinguish themselves. So that Clark doesn't have to call himself a 'human' when semantically he's not. But he is a sentient person with the same bandwidth of emotions, intelligence, devotions and ideals as anyone. And Clark Kent is an earthing because Earth is his home.
I think we tend to get lost in the sauce of analyzing these fictional concepts as if they were real people/creatures when there's a much simpler approach to all of this. Aliens aren't real, at least not in the way they are in fiction- as in Kryptonians aren't real and Martians aren't real. So why do we write about "not real" things? Well, because these larger than life concepts are avenues to allegorize human experiences. These Aliens, as a writer writes them, are meant to represent something about us.
It gets more convoluted for cape comics when tons of writers have their own interpretations and intentions for these characters but let's say for the sake of discussion that Superman and Martian Manhunter represent immigrants.
Kal-El is not human, as in there isn't a single part of him genetically that is descended from a human being. Both his biological parents are Kryptonians from Krypton. But- he does pass as a white human man. He is sent away since infancy to live on Earth, is raised by American farmers, and grew up in a culture he wasn't born in. This essentially allegorizes an inter/trans racial adoption of a first generation immigrant from one "country" to "another". Yes, Superman is culturally an "Earthling" but what that actually means is that he's culturally raised as an American. He wasn't born in America (usually...), but he was adopted and raised to be one as an undocumented immigrant.
Now let's move on to Martian Manhunter. As this character has developed in popular culture, he has grown to represent the racialized first generation immigrant. Similarly, he is a full on Martian. No human genetics, both his biological parents are Martians. How long J'onn has been on Earth is honestly irrelevant (sometimes he's been on Earth for 300 years like in older comic runs or he's a Fresh Off the Boat recent immigrant like in CW Supergirl). Because what remains consistent is that he's a full grown adult (unlike Kal) raised in Martian culture once he lives on Earth, and does not pass as any sort of human. He has to put on disguises through shapeshifting. In J'onn's true form, humans call him a foreigner. He's a fish out of water, having to learn on the spot (as an adult) how to act like a convincing "human". Sometimes he succeeds and other times people think he's odd. This allegorizes the racialized immigrant.
Think of people like Carl Lumbly, who purposefully pulled from his experience as the son of Jamaican immigrants in order to characterize one of the most iconic depictions of J'onn J'onzz. These racialized immigrants moved to America, do not pass as the White American standard, have to learn on their feet how to "act American" or "speak ""American""" in order to get by. Because of their race, sometimes these immigrants will never be seen as Americans- branded as Perpetual Foreigners even if their children were born and raised in America. J'onn too is an undocumented immigrant like Kal.
It doesn't matter if J'onn is a Fresh Off the Boat immigrant compared to a white passing raised-since-infancy to be culturally American Kal. Both see Earth, and by extension America, as their true/new home. In this, they are Americans. They aren't humans by any stretch of genetic in-universe logic, but they are both American immigrants. "Human" or "Earthling" really serve more as nationality markers rather than a denotation of racial identity.
In American media, "Earthling" really means..."American". And if we're talking Superman 2025, "human" just means "American". Because Aliens were historically meant to allegorize the fear of human foreigners.
It's important when we discuss fictional concepts to ask where these ideas historically came from, and how they can manifest in modern stories- unchecked. For aliens, that's xenophobic fears of the racialized other. Logically, in real life- we recognize that humans populate the Earth. That no matter what country you're from, we are all human beings. Even though we are different, we are all some sort of "humanity". Some sort of human centric definition of "sentience". But, defining who is "a human" is how these concepts get weaponized both in real life and fiction. It means the othering of anyone who doesn't fit that definition- painting them as barbaric animals or unfeeling conquering aliens. In real life, things like scientific racism served a similar purpose.
If alien characters are meant to meaningfully represent immigrants, then this standard of comparing them to "humanity" or a desperate attempt to label them as something they're not needs to stop. In this fictionalized context, when we equate "human" with "a sentient person with the same bandwidth of emotions, intelligence, devotions and ideals as anyone" then we're implying that Kryptonians don't have the range for such "humanizing" emotions. That any alien doesn't have that bandwidth. That these concepts are culturally unique to Earth.
And in regards to finding human equivalents, like calling Kryptonians and Martians the "humans" of their respective planets, it sets the standard for sentience and intelligence to a human centric one. When really, all we mean when we say this, is that these fictional aliens represent something about us as human beings.
It's really about being honest about what these fictionalized concepts represent- and being sure not to accidentally conflate them. Kal El is not a human, but in the allegorized context of Supes 2025, "human" means "American" and being "American" is to be "good". And in that, of course Kal is an American- raised as such since infancy with "natural kindness" (cough American Christian raised ideals cough). The problem here is how a "national identity" erases the racialized identity of Kal as a Kryptonian. But that is the point. For Kal to assimilate so affectively into "humanity" (America) that he disavows what makes him Other and Foreign.
In the same breadth, if an undocumented Chinese family immigrated to America to find a new home in this country- then they too are as much Americans as Superman is. The difference is that one of them is never truly going to be seen as American. They're visibly recognized as the Perpetual Foreigner no matter how much they assimilate. A Fresh Off the Boat European white man will be more easily accepted as an immigrant than a Chinese American family who lived in America for multiple generations. And we all know what the difference is.
As to the point about alien name species- that has technically happened! Martians call themselves ma'aleca'andrans, and in some adaptations- will have unique ethnic names depending on the color of the Martians. In Young Justice, "Ma'alefa'ak" is the name of a creature on their planet. In the Orlando comics, earthlings are called "thu'ulc'andrans".