However, my nose is decorative, and I must breath though my mouth. No repercussions as I can mountain climb.
Just search google images for "pharynx". The visual difference in size is striking.
2. Compare the aperture size of the nostrils to the mouth and throat
3. Just look at the internal structure of the nasal cavity. It's a sensory organ and designed to maximize surface area contacting the air. In other words, it's full of obstructions that intentionally reduce airflow
Your thesis here is nonsense. You can't change a downstream restriction by changing conditions upstream.
If anything, adding restriction is probably what helps. By restricting airflow upstream of the lungs, you create a partial vacuum within the lungs which probably substantially alters the conditions for gas exchange. A partial vacuum probably greatly enhances CO2 rejection from the blood, but I'm not a biochemist.
One of my biggest complaints about software developers is that so many claim to be engineers, but instead of measuring things (which is what engineers do) so many invent their own conclusions that tend to be wrong almost every time. It's disappointing.