Yes, Schultz' strategies, as outlined in her emails, were offensive and make the party look bad. With her stepping down, it will clear the air and enable the campaign to move forward unencumbered. Schultz definitely did the right thing by stepping down from her position. She violated the trust of the people.
If Trump wins the election, Schultz's incompetence as chairwoman of the DNC will be seen as a primary reason. In addition to being blatantly biased for Clinton, she let the Tea Party run rampant over congress and represented an extreme arrogance that almost matches the way Republicans portrayed democrats. Good riddance.
Yes, Debbie Wasserman Schultz' resignation was necessary. Had she not resigned, there would have been huge problems for the Democratic party. However, in this election, there is not much chance that people will even remember the problems with the DNC's emails by November. It will be a non-issue by then.
For the DNC, this election cycle has always been about one thing: Get Hillary Clinton elected. DWS did exactly what she was expected to do as head of the DNC. Now that Hillary is the nominee, DWS gets a cushy spot on the Clinton team. As terrible as it is, by November nobody will care because it will be "priority one" to stop Trump.