Design is different from the end product received in mnay situations. Design is good when it meets and solves a problem. Having a sloppily made belted case (all Amercian made brass that I've tested) is not a good answer to a problem that doesn't exist in bottlenecked rounds.
: Getting 12 loads from your .416 Taylor is pretty good. If you are shoving the shoudlers back at all, each time you load, you are not shoving them back more than a thou. or two.
: My .458 2" brass has between 60 and 75 firings per case. Mind you, pressures are lower than most magnums are loaded to and case stretch isn't bad. I am still using the original 240 rounds of brass I bought in 1976 when I picked up that rifle. After 15,000 rounds I retired the original barrel, bought a new one and the reamer. My brass has been annealed 5 or 6 times now. I do lose the odd one with a neck split. This round needs the belt and that 1970's brass was slighlty better made than today's belted brass. 2,060fps with 510gr. SP's shows my loads aren't THAT light.
: Minimum dies made today can easily shove the shoulder of a case fired from a max. chamber'd rifle, back .100". Doing this each time the round is fired, will result in splits after 2 firings. Some guys get 3 to 5 from their magnums, with some brass, not so much with others before seeing the bright ring of death.
: You are right in that excessive headspace causes spits in all types of case types. Trouble is, many bleted cases from a lot of 100 for example, already have excessive headspace - nothing to do with the chamber as it's probably within specs. Design and what you get are two different things here.
: Belts for no reason other than advertizments are of no benefit - why have them. Note that the new crowd of magnums don't have belts. Belts are an abomination on rounds that don't need them and that includes all belted bottleneck cases today. The reason they are bad, is due to sloppy mfg'ering and they give people an excuse for sloppy handloading. Wiht a rimless casse, you have to be careful not to shove the shoulder back too far. You should use the same caution with belted cases. Case life, good or bad, is the end result.