Earlier quoted context omitted.
You give as truth that #2 is not 100% morally wrong. I am not so sure, and many other people would also disagree.
The implicit assumption in what you're saying that the only way to obtain a billion dollars is by immoral means. There is no proof that this is always the case.
If a person has a billion dollars it does not exist in a vacuum. It interacts heavily within the economy in which it exists and more importantly with the people who participate in that economy.
Think for example the amount of people employed to do work in order to service a billionaire. A vast estate requires 24 hour staff, a sports car fleet requires thousands upon thousands hours of labor to produce. The logistics of a private jet demands a lot of effort from a lot of people. In order to service a single individual we require, in aggregate, countless of human lives spent toiling.
I am not arguing that the effect of increased economic activity and employment are not desirable. And one can make a decent case that a billionaire's time is incredibly valuable which to an extent may justify spending larger resources in service to this lifestyle. I just think the idea of many humans spending their lives in order to satisfy a single human is absurd no matter which societal model organizes this arrangement.
It can be argued that the people who service the billionaire are better off having found employment within or in relation to someones billion dollar estate. Though I think it is even easier to argue that we can find many hypothetical arrangements that are far more just and moral for these people.
There is also an argument to be made about the large amounts of undemocratic power that a billion dollar in private wealth entails. If the billionaire holds majority stakes within prominent industries we are delegating important decisions to opaque power with unknown agendas that we can not hope to influence in meaningful ways. As I firmly believe that a moral society is actively democratic this feels deeply wrong.
With that said, I do not have any good quick fixes. Because the reasons I outlined I feel that the presence of billionaires reveal that human society has yet to reach its moral potential. I have no illusions that reaching that goal will be either a simple or fast process. I prefer billionaires to having a nobility class. Though I hope that we as a species recognize that deeply inequitable social arrangements is something we want to move away from.