Ultimately, the goal is to make ammo straight enough to rest tension free while chambered.
Where your ammo is crooked enough to cause chambered tensions, shots are thrown.
'Crooked enough' is TIR > chamber clearances.
There is a loop here that feeds on itself, as the root cause of runout is sizing of brass thickness variance. The more sizing of it, the greater the TIR.
Well, large chamber clearances(and poor case designs) lead to more sizing (way up & back down). So you generally get higher runout in a looser chamber, but there is also more clearance -to allow for more runout -without chambered tensions.
That's how a prior poster gets by with 7thou of TIR without issue.
A tighter chamber makes straighter ammo, which is good, because it is less tolerant to runout. So then 3thou TIR hurts another poster.
Your chamber is your best die.
Brass pulled smoking from your chamber is the straightest it will ever be.
Every sizing you do from there messes this up. Often, if over sizing necks, bullet seating is sizing too.
If you cull brass with thickness variance, turn necks, and minimally size as little area as you can, you'll make straight enough ammo.
The seating plug issues are just that,, -issues. Same with press play, solved with inline dies -for neck sizing, and seating (not body sizing).
I make straight ammo with a plan to do that. So any standard V-Block runout gauge is all I need for confirmation. I have never liked anything about 'neck benders'.
But I will concede that the referenced Fli-Rite concentricity gauge is the best application of ammo straightening that I know of. It's still a v-block, and it merely nudges bullet seating, which will not affect neck tension.
It's expensive, and I don't need it, but I might pick one up someday.