Do you think that xenomorphs are bad villains because they're inherently cruel and homicidal? Or that berserk style trolls or goblin slayer style goblins are inferior villains to world of warcraft or elder scrolls orcs because the latter examples arent irredeemably evil?
First, a side-bar: Xenomorphs aren’t villains any more than hungry wolves chasing a man through the woods are. They’re threats, but not villains.
To the main question at hand though, the comment was that thinking about an entire race/culture as existing only to be cannon fodder is poor world building. It is.
Let’s take the xenomorphs you brought up. Leaving aside that the first outing featured just one (making it anything but cannon fodder; it was a Freddy or Jason or Michael Myers); the writers didn’t just grab a scary-looking piece of Geiger art and have it start attacking for no reason.
They gave it a parasitic life cycle where it needs to plant an egg in a host to reproduce. The sequel further establishes that it is only the queen that reproduces, the default xenomorph is essentially a soldier insect that exists to protect the queen and the hive.
So rather than just attacking without reason, the xenomorphs are a hive-based lifeform that attacks humans because it needs warm bodies to hatch their eggs and because when humans counter-attack they are threatening the queen/hive. Their biological drive to expand and need for human hosts makes them a threat. Their hive-based society means they respond to threats by throwing drone soldiers at them.
In other words there’s more to them than just existing as sacks of xp for the PCs to mow down.
In a more practical real-world example. The entire term “cannon fodder” dates back to the 16th century when military commanders considered their soldiers as nothing more than food to be fed into the war machine to achieve victory. Men were called cannon fodder centuries before it applied to orcs or goblins or xenomorphs.
Was every German soldier in the World Wars just an irredeemable thing born and existing for no reason other than so that valorous allied troops could mow them down?
You COULD write a game or story where every German is an evil monster that fights because they hate everyone else and want them all dead and thus the only just thing to do is slaughter them to the last man, woman and child... but such a story would be shallow (or satire) at best, and more likely be seen as the ravings of a psychopath.
You could write a game or story where orcs are willless meat robots who exist only to kill all other lifeforms... but that’s going to be shallow at best, and frankly, boring and beneath even the complexity of an old Saturday morning cartoon.
Even just adding “they were created by a wizard to get revenge/conquer the world” has more nuance (it also might make the orcs willless automatons lacking agency and destroying them regardless of their age... no morally different than smashing a tank on the assembly line before it can be used in war).
And that, I believe, is Wicked Woodpecker’s point. Evil for evil’s sake is boring and childish. Villains and even just animalistic threats need some sort of motivation beyond simple malignance. Even the Devil himself doesn’t lash out for evil’s sake, but from wounded pride and spite.