And one-way functions are not necessarily the hardest to invert. They are, in some sense, "hard enough", at least as hard as certain threshold (speaking informally).
What I meant was, the set of OWFs includes the upper bound on inversion difficulty (for functions easy in the forward direction) -- that is, you cannot remove a function from the set of OWFs by making it harder to invert (while preserving forward-direction-easiness).
