Flea had cited John Frusciante in Interview

In recent interview to stereogum Flea had told:

"Well there are a few huge differences. The number one difference is John Frusciante left the band, and he was a huge part of our creative process for a long time. I’m so grateful for him. He wrote the principal parts for many of our most popular songs, and the parts for many of our most artistically profound songs, which weren’t necessarily popular. He just gave us so much as a songwriter, as a player, as a human being, and just his relationship to music, which is such a beautiful and pure and powerful one"

Source: Progress Report