“We are all fundamentally good ... the heart itself is good,” says Pope Francis, page-9

You said it "but fundamentally good, but still open to rebellion".
Scripture teaches the opposite ->perverse/depraved.

Catholic Translations

Douay-Rheims Bible
The heart is perverse above all things, and unsearchable, who can know it?

Catholic Public Domain Version
The heart is depraved above all things, and it is unsearchable, who can know it?