If he has a turned neck chamber and sticks a unturned cartridge in the chamber what do you think will happen?
You will never understand this stuff with generalizations and assumptions.
So to be clear:
Nothing will happen while there is clearance.
If there is an interference fit, to prevent or delay bullet release, this would be catastrophic.
If that's what you mean, I never suggested doing that.
Poor neck clearance does cause terrible ES, blown primers and ruined brass.
So let's go to WHY you think these things, but with less generalizations and assumptions.
Should start with your defining of 'Poor neck clearance'. What is that?
If you mean low neck clearance (maybe 1/2 to 1thou), then you have the ES part backwards. Cases grip chambers beginning with neck expansion and working back toward webs. That's why cases stretch back to boltface. All that soot on your fired necks is gas blow back getting between case neck and chamber neck(and sometimes shoulders) -hurting consistent neck sealing. Tighter clearances of both chamber end and necks allows fast neck sealing, and the sooting is reduced or eliminated. ES/SD goes down with this.
You may find better grouping with clearances higher than I run, like if you have a lot of runout, but not because of lower ES.
Also, where necks don't seal well cases can blow back to reach the bolt face and then stretch forward (instead of backwards).
Then with each cycle, your sizing ends up different for some cases in batch.
On the pressure problems blown primers/ruined brass:
If you think tight neck clearances raise pressure, then maybe you have ideas about HOW.
How would less neck clearance raise load pressure?
You load develop with chosen clearances, right?