The interesting pattern I have seen with this type of parent, is that they often behave more like a cruel older sibling, bullying their child. They have a teenager's mentality and often a child's fear of accountability.
The unfortunate children that have to struggle with this kind of "support structure" grow up to be hyper independent, to the point that it becomes a socialization problem, or become a wreck just like their parent.
It always baffled me how people could become their child's first bully. Like, how are you going to bring someone into existence itself just to fuckin torture them?