Switching was (as always) much less significant than turnout.
And the previously absolutely dominant neoliberal faction of the Democratic Party hasn't made a lot of substantive (and even more symbolic) concessions to the anti-establishment progressive faction of the party because of a sudden outburst of generosity.
Just because Democrats (and plenty of Republicans, though mostly it's only the ones not currently in elective office, or on their way out, that talk strongly about it) notice and are outraged about foreign interference doesn't mean that they aren't aware of and actively seeking to address other issues that hurt them in 2016. There's nothing stopping them from doing both.
If I remember correctly, it wasn't so much that many people switched parties, but that typical Democrat voter turnout was low, reflecting some amount of disillusionment.
Also, what you say about the Democrats' identity crisis seems to mirror what's been happening with Labour (the left party) in the UK.
Disillusionment through propaganda and well-timed leaks of stolen documents by a foreign, hostile power.
You could ask yourself why the Russians penetrated the RNC but decided not to release any dirt. Perhaps you could ask yourself if this has any bearing on Trump's Russia stance? Could he be unable to admit meddling for fear of undermining his very legitimacy? As a result of this is the head of state feuding with the unanimous conclusion of his (+allies) intelligence agencies good for anyone? Who would that be?
This is why the source matters. Because things are always leaked with intent, and by missing that intent and being distracted by shiny talking points you're missing the whole story. Both matter, equally.
Why do we have to "presume" they do about Trump and "know" they had some goods on Hillary?
But no, they rather blame others, be they foreign or even within the party: right now the Dems can’t decide if they are 1980s Dems or 1920s Workers Partiers.