Frank,
I think some of it has to do with positioning on the string......I think the majority of the damage comes from conatct with the cables on the forward stroke and then ripping as the string comes back to brace.

700-800 shots on a high energy bow sounds good to me for Leeches , or Bowtech products.
To work properly they have to be pliable, unfortunately it's that property which makes them susceptible to damage.
I look at Leeches and the like as a temporary item everytime I put them on. They WILL die eventually.

I have had good luck with the 'Crossbow/Compound" SIMS leeches over the traditional "Z" shaped ones.
They seem a little tougher over time.

Nothing else rubber beats a nicely served in and trimmed cat whisker ball for durability though.