Use does not necessarily constitute abuse. And, the 870 is based on John Browning patents, which automatically means it's tres overbuilt.
I've seen exactly one pump that had been abused and the action bar bent. It was the late and unlamented Winchester 1200, place was the Md House of Correction. As near as I could deduce, one of our less intellectually gifted but muscular officers had tried to rack it w/o hitting the slide release.
One of the 870s here was purchased by my father, used, around 1956. it must have been one of the first Wingmasters built. I've personally put over 3000 rounds through it. While the finish isn't as nice as it was, it still locks up like a bank vault.
JB Browning didn't design trash(G)...