Complex sentence: He was viewed as most likely to continue the Second Vatican Council, which already, without any tangible results, had lasted longer than anticipated by John XXIII, who had a vision but did not have a clear agenda.
Split into simpler sentences: He was viewed as most likely to continue the Second Vatican Council, which already, without any tangible results, had lasted longer than John XXIII anticipated. John had a vision but did not have a clear agenda.