I don't think the tag was necessarily intended to be mutually exclusive from personification, but it was at least intended to cover characters that were already very near human and turning them outright human. For example animal girls/boys (i.e. human with animal ears and tail), elves/other pointy eared races, dolls (like the Rozen Maiden girls), androids, etc. Such transformations could be extremely minor, such as simply removing a character's pointy ears or removing a few lines on the skin of an android, so I can't say all cases of humanization inherently were personification, at least as I had understood it (which doesn't have to be correct).
Personification as a tag is rather broad on the type of transformation involved, covering anything from a cat turning into a cat on their hindlegs legs wearing human cloths all the way to a spaceship turning into a full fledged human wearing sci-fi gear on. Humanization on the other-hand was intended to be a specific transformation where you take a character that was already human-ish and strip them of anything that made them non-human, and thus becoming full human. (Going by that kind of definition for humanization, you could alternatively look at it that the character being transformed had to be human enough to be viewed as essentially a human with some additional traits.)
The issue Veradux brings up is really how the site has changed and grown, especially the increase in ESL users and perhaps also simply newcomers who may be more inclined to judge tags off of their name alone. That's not something that can be easily resolved for very niche and specific concepts, outside of trying to keep them into consideration when naming things. In this case the tag being named humanization is likely misleading as it doesn't cover all cases of "becoming human" or it's easily being misinterpreted as to mean "becoming human-like." In this case the current humanization tag would be more accurately named something like humanoid-to-human_transformation.