I don't think it's that FL sizing is more accurate than Neck sizing, but rather that FL sizing isn't less accurate than Neck sizing and is generally more reliable for their type of shooting.
It’s mainly that FL sizing is more consistent shot to shot than neck sizing. Brass doesn’t always blow out exactly the same and the fact that these guys quite often use just enough neck tension to hold a bullet, then finish seating with bolt closure in other words a predictable jam, so it’s the feel of bolt closure.
Secondly I do wish people would realize that the guns they are using have absolutely nothing in common with a factory hunting rifle unles you go hunting with a 4000 dollar gun with a 3000 dollar scope on it. Sitting on top of a 1000 dollar rest. Special built for just one purpose. Tiny groups.
Hunting rifles I FL size always for feeding reliability. Varmint rifles get both NS for 4 firings FL to bump the shoulder plus anneal on the 5th because I don’t really care about reliability since most of my varmint rifles are single shot. AR get FL every time again for reliability reasons.
My bench guns got FL due to the reasons stated above in paragraph 1.
Do what you want for the situation and whatever works best for you. There isn’t a one size fits all here.
