The sharper shoulder does increase brass life, but only if you neck anneal now and then.
About every 8 shots is good. If you do that the brass life can be about 2X more than a standard shell.
The brass on a standard shoulder flows forward easier than it does around a 38 or 40 degree shoulder but the splits you get in the neck are not affected by the shoulder angle.
In my 44 years of gunsmithing I have made many Ackley Improved chambers. If I made a guess I'd say about 75 of them. I have a lot of experience with them and I had the honor of meeting old man Ackley in person and having some long conversations with him.
But today I believe A.I shells are a tinkers delight. Something to play with because we like to play.
The “reasons” for doing AI chambers are largely a thing of the past. Those reasons are now all covered by factory rifles and factory chamberings. AIs can still be fun, but if you like to site brass life as a reason remember the cost of the dies and the reamerand the need sometimes to open up the feed rails to m,ake them work (paid for by you) and compare that to the price of just buying 2X the brass in a 25-06. Standard chamber from the factory and a set of $32 dies and your set for the life of the barrel.
The most important focus P O Ackley had in his early experiments was to duplicate 25-06 and 6.5-06 ballistics (before the 25-06 was a factory round) when there were hundreds of thousands of KAR length Mausers available very cheaply. The KAR was a shorter magazine and Ackley wanted to use the standard 57mm length Mauser shell as his base case. The AI experiments were done with about every shell at one time or another, but for the most part the 2 that were the greatest success were the 257 AI and the 6.5 AI
Now days you can buy a 25-06 over the counter as well as a 280 or a 270 and buy the lower prices rifles for less than you can buy the parts to do a Mauser in an AI shell without any rework of the action to feed, no custom dies and no custom chamber reamer.
If you like to tinker and you do the work yourself the AI can still be worth your time and efforts but if you are paying a gunsmith to do it for you, you are going to pay a LOT more money to get the same ballistics you can get with a 25-06 by building a 257 AI. And you will get a bit less than a 270 Winchester will give you if you have a 6.5 AI made.
The days of the $30 surplus KAR are long gone. I still prefer the old M98 action over all others for my best custom bolt guns, and I will still build on a good KAR or a GEW, but the idea that the AIs are going to be something special is really not true. It’s fun, so if you like them, use them. But if you are looking for a faster bullet there are a lot of easier and cheaper ways to go.