I doubt that shooting soft will wear the tip sooner. I shoot all types of shots, including power shots, so I guess it all comes down to how much we're willing to tolerate as the tip wears down. I feel it immediately once my tip wears past a certain point because I have to work harder. That's my gauge for when it's time to change the tip.
I didn't mean that shooting softer would wear down the tip sooner. I meant that shooting softer (plus using a soft tip) would make it take longer to sort of - break-in your tip. Therefore, you would have to shape it more often to keep it the radius that you like. The shaping of the tip would be what would shorten the life span of the tip. Not the soft shooting.
I read in a recent AZ thread that even the soft tips end up at or near the same hardness level as do the harder tips. They just take longer to get there. It's the process of hardening up the tip that cuts its life short. At least that's my theory.