Complex sentence: He was said by his contemporaries to have been the most technically advanced pianist of his age, and in the 1840s he was considered to be the greatest pianist of all time, although Liszt stated that Charles-Valentin Alkan had superior technique to his own.
Split into simpler sentences: He was said by his contemporaries to have been the most technically advanced pianist of his age, and in the 1840s he was considered to be the greatest pianist of all time. Although Liszt stated that Charles-Valentin Alkan had superior technique to his own.