I believe your argument is that we should never have clear-cut legal boundaries on anything where there isn't a clear-cut, justified reason.
If I understand you right, you also believe there should be no specific age where people can vote, or drink, or become US Senator. Because what's special about being 18, or 21, or 30 years old? Nor age restrictions on when someone can decide to get married.
There should be no progressive income tax, because what's special about each boundary?
There should be a gift tax on all gifts, with no special change at $15,000/year - or no gift tax at all.
Note that the latter two are meant as ways to address your #1. Getting rid of them requires coming up with alternatives ... and I don't see any good alternatives.
I disagree with the basis for #3. I want my government programs to be equitable, fair, just, transparent, predicable, .. and rank 'efficiency' as a far lower importance.
And I feel that asking questions like "should billionaires exist" to be important in understanding why it is that, for example, Gates and other billionaires have an outsized, inappropriate, and anti-democratic effect on US school systems.