For generations the Philadelphia Orchestra was one of few institutions in this town that could claim a world-class status, and even for the many citizens who could care less about classical music, this was a source of pride. Today, it’s hard to find similar pride in an organization so attached to a nostalgic, often reactionary vision of its own history. There is room for lots of different kinds of music in our big city, and maybe it is for the best if the Philadelphia Orchestra is no longer at its center.