re HRC and the DNC... That’s just not how it works. There is no monolithic “Democratic Party”. Just loose coalitions of power centers, big and small, that brand themselves as “Democrats.” And 1/2 of “party politics” is always the candidates parasitic relationship with the various interest groups, making promises to earn endorsements and contributions, to be forgotten once elected. Use them and then disgard them. There is nothing (comparable to the right) on the left where elected are held accountable to their constituents.
If voters want more choices, then they have to lower the barriers to entry, by (greatly) reducing the cost of campaigns. Public financing, restore fairness doctrine, time box campaigns season, universal voter registration, compulsory voting (most campaign money on the left is spent on GOTV), etc.
Similarly, yes, all those things you mention were part of the context in which the 2016 election occurred but they were decisive only because that Democrats picked the weakest possible candidate, with higher unfavorable ratings than any previous major party nominee, firm unfavorability because of decades of national political exposure, and relatively little experience as a candidate in electoral politics (having only served a couple terms as a Senator in a heavily-selling state coming in onethe coattails her husband's Presidential popularity; she'd never been in a campaign where she needed more than the approval of the Democratic establishment to win.) Clinton had the worst negatives that can come with long political exposure, without the strengths that come from long and relevant electoral politics experience.
And, no, it's not her fault, it's the Democratic establishment's fault. Clinton didn't have the choice to be herself or be someone else, the Democratic establishment did have the choice not to decide to go all in for Clinton even before other candidates were declared.