I think any friction advantage smaller diameter arrows have is a minor advantage at best, and is way overtalked and overblown. IMO, the lubricity of body fats and fluids would minimize any real advantage smaller arrow diameters would have.

Also, when you start talking smaller diameters, that generally means carbon vs aluminum. That also generally means the smaller diameter arrows are significantly lighter arrows. Significantly lighter arrows carry significantly less momentum. So, the friction advantage of smaller diameters is even more offset by their lower momentum values.

Comes pretty close to being a wash, as far as I'm concerned.

Now, if you weight those skinny arrows up to weighing in about the same as a 2216 to get their energy and momentum values up... Then we can start looking at arrow diameter as more of a major player when it comes to penetration.