My K1 has been running for 5 years. Actually longer because I bought it all used. I don't see any evidence of what you describe. I'll keep an eye out and look for signs. All pieces are firm to the squeeze. My system has not behaved in the way you describe, asking my friends who have used it longer and they say the same.
I've heard of people running it for over a decade.
Massive industrial Koi farms use this product. Huge waste water treatment facilities use this product in massive amounts. Beyond the scale any of us use it in. It must be possible to design a system that does not have the problems described? Has anyone else noticed their product break down? I've never heard of this before, but would like to know more.
Would you recommend I replace my media as it is well over 5 years old? I would do so preemptively if needed to prevent disasters.
Look at the industrial application