Looking back on any election in history, it is easy to find winners who were described as arrogant. Arrogance does not have a lot of bearing on a candidate the public deems qualified for a position. Many of Clinton's critics also call her arrogant when she uses the same tone or position another candidate may utilize, often using derogatory words to describe her because they do not believe a woman should behave like a man when it comes to leadership.
Hillary Clinton has all but won the nomination already, and it is now just a matter of technicality. Once she hits that magic number of delegates, the race for Democratic nominee will be over, and I believe that Hillary will come out the winner, despite how many people feel about her personality.
At this point, there are no good choices, only the least among evils. Trump is about as arrogant as they come. Hillary is smart, experienced and understands how politics work, or don't. If voters are choosing based on least arrogant candidate, Sanders has to be it. Trump can't tolerate any opposing views and broadcasts that it's his way or the highway. Hillary may be viewed as arrogant, but she's not threatening her detractors in the same way Trump is.
Most politicians are arrogant. I don't think that Hillary Clinton being seen arrogant means that she will not win. If she does not win the election I think it will be more related to the fact that she is a woman and seen as arrogant than to just seeming arrogant. The combination in today's society can be detrimental to a career in politics.