You must have found your way over here from LRH.
What's LRH?
Caveat: I've never slo-motion filmed a clear plexiglass barrel...
But... Peak chamber pressure (heat) is usually reached with the bullet about 2 inches forward of the case mouth, and in most cases pressure drops to below 45ksi ~6-10" down the bore. The pressure/gas that is behind the bullet is more or less equal in the pressure vessel (bore area) behind the bullet. Bore scope a high pressure rifle barrel that has 1000+ rounds on it and you'll see that bore condition at about the 10" mark starts looking almost brand new, despite the first 6-8" being a fire-cracked wreck. Also bore scope low pressure barrels (9mm, 45acp, for example) that have tens of thousands of rounds on them and observe the relative lack of damage. Unless someone can provide hard data to the contrary, I'm going to sincerely doubt that shoulder angle or neck length has much of any bearing on throat life, and that loading to over 50, 60, 65ksi with 40-150gr of powder has a LOT to do with it.
YMMV. Years back I bit on the "2500 rounds no problem" bait on the 6.5 SAUM and dumb asses touting "3000 rounds & 3400fps" with the 6mm Comp match [effectively a .243 AI] with its "cool burning slow powders" etc. etc... My personal results fell exactly in line with what common sense should have told me from the get-go.
My point is case efficiency is one of very few variable that improves barrel life. Its asking a lot to get life from a magnum, lol.
Burning 6 grains less powder for the same bullet and velocity in a 7 ss vs a 7 rem mag is meaningful, AFAIK, it will reduce barrel erosion.
Heat is a contributing factor, barrels do "burn up" whatever the process.
I see how peak pressure correlates to firecracked areas, but I don't think it is causation. Firecracking and throat erosion are not the same. Though they interrelate.
All the smart kids talk about the gas and powder molecules doing the abrasion to the throat, not just pressure/heat per se. Firecracking contributes, sure. Also I don't see how it is pressure alone because a .308 and .243 can be shot at the same pressure, the SAMMI .243 is actually lower than .308, but the .243 will erode faster. It is not pressure.
Less powder burning reduces throat erosion in the same bore, AFAIK. As I understand, case efficiency reduces powder charge. It is at least one variable why the 6xc has better barrel life than .243. My position on case efficiency stands thst it increases barrel life.
Proportionally, a magnum is a magnum and the benefits are reduced, but rhey are still benefits.
Now, neck length and shoulder angle "focusing the flame" is more hotly disputed. I may be on the losing side there and for argument purposes I will concede that may be correlation without causation. Erosion differnces may be 100% caused by reduced powder charge, which comes with case efficiency differnces. No one really knows AFAIK.
Certainly the case shape is the difference, but it may be the amount of powder is the only or the primary reason 6xc has better life than 243.
Bottom line, guy wants a magnum and barrel life. That is a hard ask... lol. 28 Nosler was on his list, and that's why I gave the 7ss. Its a balance, clearly better than the 7 rem mag, and clearly not as bad as the 28 nosler.
IMO case efficiency also correlates to precision, but that is another argument altogether...
The one way to squeeze as much barrel life as possible is to choose a case as efficient as possible. Short magnum cases are one way to get a smaller screen door on rhe submarine...
