With the rise of militant secularism, Rome and Moscow make common cause
But:

The deepening relationship does not portend a union between Roman Catholicism and Orthodoxy.

Right.

Roman Catholics are more optimistic about unity because they are less aware of the historical animus that exists between Catholics and Orthodox.

That’s not why union can’t happen. This is. Sacramentally they’re the same but ecclesiologically the difference is an inch apart but infinitely deep: impossible to reconcile without one side caving. (Like Catholic infallible church vs high Protestant fallible church. Union will never happen. The Protestants have to convert.) I hate Orthodox anti-Westernism but don’t want to see them turn into Eastern Novus Ordo, which Greek Catholicism really is.