The mining meta has changed. In 2013 it was about squeezing max perf out of cards at any cost. Now the focus is on efficiency. Most miners will undervolt and underclock cards.
In this scenario, cards used for mining see less heat cycle stress than the cold/hot workloads a typical gaming PC sees. The primary stress is on the fans. However, even those are rated for 5-10 years MTBF under constant use.
I might buy the idea that miners don't stress their cards like the other person said, but I'm not convinced by your statement that running an electronic component hard for long periods of time won't increase the risk of failure. Especially in something as high tech and compact as a GPU.
If you are looking to buy those used GPUs for cheap you should avoid any public language that tries to downplay the impact of 24/7 mining.