The way you framed those two quotations is misleading to say the least. Clinton did not make that Tweet as a reply to Trump's tweet, his was from 2014, and hers

The way you framed those two quotations is misleading to say the least. Clinton did not make that Tweet as a reply to Trump's tweet, his was from 2014, and hers was from 2016. So, your statement, "Twitter isn't public discussion, unless you consider the following examples of discussion:", does not follow. You also say that "unless you consider" the aforementioned quotations to be public discussion, you therefore can not possibly view Twitter as a tool for public discussion, which is a false dilemma. I agree with your last line though about Twitter being censored in a similar fashion to Facebook.