Three high-profile Boston arts organizations have recently come under new management, and while that’s the type of upheaval that can potentially lead to a downgrade in quality, at least in the short term, the opposite has been the case, according to Ed Siegel. The new Boston arts leaders “have responded to the challenge by seizing the moment. The Boston Symphony Orchestra, the American Repertory Theatre, and the Boston Ballet are all in the midst of seasons that are energetic, daring, and smartly crafted.”