My take on codependency is that it is a set of learned behaviors (coping mechanisms) that can be unlearned.
As do I, but i happen to believe (not that it makes any difference to anyone including me) that a set of behaviours is not an illness, mental or otherwise, and unlearning them is not dependent on them being collectively given a "sickness" label.
I may bandy about the words insane, crazy, nuts, but I don't think of them describing an actual mental illness, I am "crazy" in the same way that I have a "crazy" day or an "insanely" expensive treat.
I have had many tussles with mental illness and although co-dependent behaviours can make me more prone to mental illness, it isn't the same thing. Why medicalise a set of coping strategies/learned behaviours?
I feel no stigma regarding my depression, or the hallucinations that untreated depression leaves me prone to.
But it's a bit like describing all growths as "cancer": they may share common features and sometimes they can lead to cancer, or look like the same thing, but they aren't cancer.
I feel different about "abuse"; that I admit to, but feel shame about, I feel the need to follow it with a quick "but he was worse" so I take your point there.