I'm looking at this as person who likes to ground things in reality when it comes of sci-fi. After all, all the best sci-fi is based on real science and biology and straying to far outside of the realm of possibility. That is the difference between science fiction and science fantasy. I'm looking at things as if they was real beings living in a real ecosystem. How can you go about living on a planet and fighting an enemy race if you don't know the first thing about them? Realistically as Humans are trying to get a foothold on the planet to make a home and protect themselves there would be people trying to study all the new lifeforms they run across both as way to learn more about this world but also to make sure of those lifeforms pose any threat or threat or benefit to them ether actively or passively. And basic questions like how a lifeform reproduces, as well as if there is any kind of sexual dimorphism in beings that have different sexes are among the first things you ask when studying a new lifeform along with how do it grow and change over time.
If helps try to role play as a scientist or biologist who just found a new type of lifeform. How would to go about telling other people about it and how they can identify others of it's kind? And if they are noticeable differences in how their bodies look does those differences makes them any more or less of the treat than normal?
Or they could only have one sex, so they all look the same...and the aliens sexuality doesn't need to factor into the game.
Sure you can have a races of beings that at are all asexual so they are basically clones of one another. But I view that as lazy writing and world building that shows a lace of imagination on the part of the creator. For one if you are going to do that rout how to explain away one of the key problems with such beings like that, population control?
In nature the way such beings are kept in control so they don't have an overpopulation crisis are ether by predation, meaning they can't be at the top of the food chain because something else has to be able to hunt and eat them or they are at the top of the food chain but are also cannibalistic by nature and eat each other. Or by having tightly controlled life cycles influenced by things outside of their conscious control. Such as the patterns in their planet such as seasons, the gravitational effect of near by objects like moons and other bodies on their planet, as well as things like strong cosmic rays made by other near by stars and blackholes, and/or by having an internal biological clock linked to body's self destruct function as their cells are programmed to die when key conditions are met (the self destruct function or kill code as some people call it is part of the body's immune system and even Humans have it). Or do to the fact that they are all clones all it would only take is one pathogen to kill off the whole population and they would have to hope at least one of them can mutate in the right way with an immunity to it so the whole race doesn't die off. Or a mix of all those things listed and more. I'm not saying it is impossible for it to happen, only that odds are against a race of being like that becoming anything that spacefaring humans would see as threat because of easily exploitable biological weakness. Plus there would be no biological variations in such a race as they would all be clones. So if you wanted to say give one them horns or claws or anything else you have to explain why they are so different from rest of their race as one small change would not make a new complex body part from nothing.
If you want to have one race of beings where their are notable differences between individuals you need to have driving force behind such changes. Or make it so their DNA, or something else like it, has parts in that randomized but in lifeforms with such randomized parts to their genetics the things that are randomized are insignificant to their overall health and survival. Like the fur color and pattern of house cats for example, If you make a clone of a cat each clone will have different fur colors and patterns not only from the parent but from each other too because that part of a cat's DNA just naturally randomizes itself. Outside of things like that you would need to explain why in this races of beings does this group of them have stingers or spikes and this one doesn't.
Lol, I love applying real science to video games, movies, and stuff. It is so much fun. Even more so when apply it to an already ridiculous idea but think through it as if it is something serious. Hell, back when I was in my freshman year in college made a paper about the legality of suing Santa Claus for things like breaking and entering as well as for things like breach of contract. The breach of contract being for him not giving you thing you asked for even though out was good that year. Lol, power of an analytical mind used to explore humorous topics is always something to behold.