>>8
That was a mistake in hindsight though, one of the disadvantages of distributed networks is that they are harder to moderate effectively. That's why, over time more and more of the instances that were created as "Twitter without Nazis", contemplated de-federating or whitelist federation, which stood in conflict with those who were interested in a distributed network for technical reasons.
>>8,11
I think you're close, but you've over specified. In abstract terms you might say that Mastadon's distinguishing characteristic in contrast to Twitter is better power relations, as in users and communities especially have more control.