Complex sentence: Traditionally he was considered the model for the hero of "Tale of Ise", which contains many of his waka, although not all waka in it were his works and some of its episodes can hardly belong to his real life.
Split into simpler sentences: Traditionally he was attributed as the hero of "Tale of Ise" which contains many his waka, not all waka in it were however his works. Some of its episodes can hardly belong to his real life.