I think you're modeling epistemic rationality as an externally assessed attribute and I'm modeling it as a skill.

Not really. I am modeling epistemic rationality as a sum total of skill, and biases, and willingness to look for quality evidence, and ability to find such evidence, etc. It is all the constituent parts which eventually produce the final model-of-the-world.

And that final model-of-the-world is what you called "an externally assessed attribute", but it is the result of epistemic rationality, not the thing itself.