Could you explain what this missing element is missing from, and what it should supply?

At that time, I was keenly experiencing the lack of an objective morality in the materialist worldview.

You seem to be expecting "rationality" to replace "God" in some slot; perhaps "theory of everything". But this seems to me a category error, rationality being an activity, not an explanation.

This is exactly correct. I thought 'rationality' was a paradigm to replace a religious worldview. I probably meant 'materialism' everywhere I used the word 'rationality'.