No version of D&D hews to the morals of ancient or medieval cultures. Never has. Look at the definitions of Law and Good in any edition and that is most certainly NOT ancient or medieval morality. Not by a long shot.
But, the argument that we shouldn't have minion mechanics because it's morally wrong? Uhh, no, I'm not buying that one, like at all. Not even a little. Never minding that you can have construct minions or demonic minions or undead minions, all of which you can make a fairly solid argument that there is zero morality involved in destroying any of them, the rabbit hole of "killing is immoral" is not one that is going to be settled by D&D alignment.
Either killing is evil, so, killing ANYTHING is evil, so minion or not minion doesn't really matter, or morality is more nuanced and we cannot make blanket absolutist statements, in which case minion or not minion doesn't really matter since it's going to depend on so many other factors that how many HP a monster has is so far down the list of criteria that it might as well not exist at all.