The wiki clearly explains the abomination as a creature that is concerned with nothing else but malice and destruction. You cannot claim Uldred and Baroness are same as Anders.
I can, however, question the objectivity and accuracy of the in-game lore, which the wiki relies on. Thedas doesn't even have a concept of psychology, but from what I have seen and inferred I believe psychology is the most relevant subject when discussing spirits.
If Uldred and the Baroness were capable of of things other than malice and destruction, and they very well seem to have been (albeit their pride colored things), then I would certainly draw them as subject matter for Anders rather than an archaic and absolutist definition by people who teach that basically apply retroactive tautological classifications on spirits and demons.
By broader definition spirit healers are "abominations" too but there is a clear difference between these abomination and Uldred and Baroness. Abomination somewhat has two meanings here, first ones means simply possessed and the second ones is used on abhorrent possessed beings. The question is was Anders the 2nd variety? Wynne is directly called an abomination in Asunder, is she the abhorrent being the Baroness was or was she in a similar case as Anders (more or less better and more in control but same nonetheless)?
Given that the Anders of Act 3 murdered a lot of innocents for the deliberate purpose of sparking a massacre in order to generate a revolt he made no preparations to prevent becoming a third, even greater massacre...
Of course, the nature of demons and spirits is already known to be misunderstood (Anders fell to that one), which the subject of spirit possession is such a taboo that no one in the Chantry really understands how it works. What we have seen seems to indicate that abominations (spirit possession) sees the subject influenced by the aspect of the spirit in question, and vice versa. Uldred and the Baroness were influenced by various forms of pride. Merrill was playing with and being played by a spirit of Audacity.
We also, from Anders, see that the host and the spirit can influence eachother. It's not simply Justice turning into Vengeance. Before the merge, Justice was pretty broad and even contradictory, focusing on any apparent injustice of the moment over any prioritization or unifying theory. This is the spirit that accussed Anders of enslavement, after all. After the merge, however, Justice would only really respond to the subject of mages, Anders' personal fixation. And likewise, Anders himself was moved and pushed into being a more active actor by the influence of Justice.
The influence of spirits on their hosts appears to be the true impact of abomination-hood. Sometimes the effects an be delayed (Anders and the transition to Vengeance), sometimes they might even be benign (Wynn's spirit of Faith bolstering her, well, faith). The demonic abominatiosn we've seen also fit that model: Uldred and mage-pride, the Baroness and her pride in appearance even after her possession. But regardless, it does appear that spirits and demons both do influence and exagerate the psyches of their hosts.
If that is true (and we can't say for sure: only the Rivian shamans would be an authoritative source), the idea of 'abomination as an abhorent being' is outdated and misleading. It puts an ex post facto label on something's effects, rather than its nature. Demons become demons because they're bad, and you know they're bad because their demons. It breaks down the Chantry's arbitrary system when the definitions become less descriptive and more aspirational: Justice can become a Demon through Anders anger, so maybe a demon can become a spirit, and maybe had someone else taken in Justice everything might have changed.