> Democracy is about (in theory at least) giving each person a meaningful say in their own governance, which in turn implies not allowing any single person to become too powerful.

this is "direct democracy" and it's not even close to exist in USA... even with that a society can allow powerful people to exist if they don't create any law forbidding that

Democracy includes a broader array of governmental organization than just pure direct democracy. If you do believe that individuals should have some ability dictate the terms of their own social organization, then you believe in some amount of democratic principles.

Economic power eventually manifests in the political realm. The wealthy effectively get more votes, which means that society moves away from being democratic. Thus substantial wealth inequality is incompatible with democracy in the long run. We have been witnessing that corruption for a while now.