That process is called metal fatigue and we don't load our rig up with that much most of the time. Sidestays are typically loaded between 30 % and 50 % this increases the number of cycles before breakin enormously. Besides the magnitude of the change of loading is also important. You are talking about full release after each 75 % load. On cats the amplitude is much smaller.

I've been sailing with my Prindle 16 stays for 7 years and I bought the boat secondhand. Never had a problem and I sailed that baby alot.

Replacing every 2 years is too often for recreational sailing.

Wouter