http://fivethirtyeight.com/features/how-berned-is-bernie-sanders-by-the-dnc-data-breach/
So yes it was significant enough, whether you think he actually used the information or not gathered by those four people is up to you.
There is a reason for this suit and certainly if it wasn't filed what are the guarantees they wouldn't have locked his campaign out of information for more than 24 hours.
There's a reason for the initial suit and why he wasn't criticized for it at the time. But it was 24 hours only and gave his campaign the optics of standing up to the DNC. The article you're quoting basically says that it would be immensely damaging... over the long-term. With the benefit of hindsight that it was only 24 hours, he's pushing the lawsuit again. That does not make him look good.