I was trying to show that it is not "merely a legal expedient", that corporate personhood had a specific purpose, and that it differed from a real person. I think that the confusion about legal personhood in corporations comes from how lawyers explain its existence. A couple of lawyers I've had explained it as, it's just like a person in the law, except where it's different.
The problem is that we haven't created a clear enough distinction between a natural person and a legal person. In many cases, corporations have rights but not the responsibility. For example, they have speech rights, but they don't go to jail when the corporation commits a crime. The judicial inequalities between ordinary people and rich people are even greater between natural persons and corporations.