I was not aware that a straight case was needed for long life.

I shoot .40-65 which is strongly tapered from the same head diameter as .45-70 with full length sizing at every cycle. The only case loss has been from bending a few case mouths not well aligned with the die.
Likewise .38-55 which has less but not zero taper and I am still using brass bought with the rifle about 15 years ago.