The concept of corporate personhood is way older than you think, it goes back to at least ancienct Rome around 800 BC. Other countries have that as well, eg. the German constitution says very explicitly “Fundamental rights shall also apply to domestic artificial persons insofar as the nature of such rights shall permit.”. That’s not really the issue, the actual issue is the extreme reliance of political campaigns on donations coupled with the exorbitant costs of political campaigning in the US.

Citizen’s United is very often misrepresented as being about corporate personhood, when in fact this concept isn’t even referenced in the ruling at all. Instead the ruling says that political speech rights aren’t contingent on the identity of the speaker at all. Even if you abolish corporate personhood (which would bring a whole host of other issues with it because for example corporate property ownership hinges on the legal person concept as well) that still wouldn’t overturn Citizen’s United.