It’s our term “wife” that I object to as a way for defining anything in Homeric times. The inherent division between παλλκαίς and ἄλοχος is obvious. But our marital arrangements just don’t look like theirs.
For pre-legal societies like this, the wife/concubine division was very close to hierarchical polygamy, with a single chief wife in a far superior position to the others, who were basically servants or slaves. Until later legal systems codified it, this chief wife position was inherently unstable. The position was secured by: 1) a woman’s in-laws, 2) male children, 3) social mores, 4) her husband’s regard.
I think that the instability actually explains a few of the features of the poem.
For example, concubines are generally taken from lower social brackets and war captives, with concubines of the same social status being a serious threat to an established wife. Absent an established wife, the difference between a concubine and wife is almost entirely up to the whim of the male. So maybe it’s not all that strange that Achilles is the one to call his war-bride an ἄλοχος. (She may well have found that position hard for her to keep once he got her home, though.)
A concubine that is honored above an established wife by her husband has a high possibility of displacing her (absent family or heirs to protect her rights). This seems very close to the Clytemnestra and Medea stories.
For Homeric society, Odysseus’ philanderings are in stark contrast to Agamemnon’s crimes (although he may seem just as bad as Agamemnon to us today). Unlike Agamemnon, Odysseus has done nothing to threaten Penelope’s position as his chief wife. In fact, he confirms it every chance he gets. Sex is entirely beside the point.
The explanation for Calypso’s language, I think, is that while we define “husband” as an equal term opposed to a “wife”, that simply isn’t the case for their society. While there was a παλλακίς/ἄλοχος distinction, there was no similar relationship hierarchy for men. ἀκοίτης for Calypso does not mean “husband” in its eternal sacramental/legal bond sense, because there was not really a distinct category for that for her, as opposed to us with our clear “boyfriend/husband” division.