Complex sentence: Ernst was widely seen as the superior violinist of his time and Paganini's greatest successor and that he not only developed the polyphonic playing, but also discovered new idiomatic ways to compose polyphonically conceived violin music to a degree that is unprecedented to this day.
Split into simpler sentences: Ernst was widely seen as the superior violinist of his time and Paganini's greatest successor. Not only did he develope the polyphonic playing, but he also discovered new idiomatic ways to compose polyphonically conceived violin music to a degree that is unprecedented to this day.