The City of London allows corporations to vote because its existence as local authority predates anything else that exists in the UK. Mentions of The City of London's special rights exist in the Magna Carta, and it was never included in any of the local authority voting reforms the occurred since its creation.
The local population number have absolutely nothing to do with the existence of corporate votes in The City of London. It's not even the smallest local authority by population, the Isles of Scilly are, and corporations have no votes there.
Sure but if the City had turned out to be full of people, those ancient rights would have been modified to suit the requirements of modern democracy. The City’s unique form of governance is only possible because it is predominantly a commercial district.
No I don’t think it would have. The City is fairly exempt from being fiddled with by parliament due to its direct relationship with The Crown. I don’t see any reason why the The City would give up its rights without a substantial fight.
Given its small area, I doubt anybody would ever be interested enough in fighting with The City to revoke its ancient rights, and independence from the broader UK government. Past monarchs and leaders have attempted to strip The City of its rights, all of them ultimately decided it wasn’t worth it.
The local population number have absolutely nothing to do with the existence of corporate votes in The City of London. It's not even the smallest local authority by population, the Isles of Scilly are, and corporations have no votes there.