Brass is a complicated thing. Even brand new brass from the same batch has variations as it's an extruded material.
New brass will usually be good @ 1st firing, but much better afterward for three perhaps four firings. Then it should be anneald to retain optimum seal (obturation) & spring back. (Not a complicated process)
The seal is important to maintain consistent pressures round by round.
Retaining the fireformed concentricity and headspace by neck sizing is a short term solution to maintaining accuracy.
In my view, it's better to full length resize to your fired case headspace dimension. Doing this will produce extended case life.
It's not hard to set your f/l die to do this. You'll find how to set headspace on f/l dies all over the internet. It's also important to set your f/l die properly so that the decap rod doesn't offset the case neck from case body....thereby upsetting concentricity.
Once the set up is done, by sticking to a routine of annealing each 3-4 firings, full length resizing without bumping the case shoulders back more than .002", with the right load recipe for your rifle, your accuracy should be pretty damn good....all other aspects of gun care permitting.
However, this is only a first aspect of what's required with brass prep. The care you take and attention to detail is also a great help and will aid consistency. Consistency is what produces time after time accuracy.
A final point after seating the bullet is to maybe use a Lee Factory Crimp die, a consideration to 'even out' neck tension.