Interesting. I came back from a northern trip and looked for a new outdoor hat in a sporting goods chain store. I impulse bought a #9 out of curiosity. This thing is quite cool and with a few swipes on my Sharp Maker, it's a freaking straight razor !
Yup.
Now try to break it.
Obviously, don't put massive amounts of closing pressure on the handle with the blade locked. The lockring will pop off and it will close on your fingers. But then, why would somebody put massive closing pressure on the knife?
But, pry, twist, cut hard and do all things that normally cause a lock mechanism or joint to open up and start to wobble.
I've not been able to produce any blade play in any of my Opinels. Typically, you'll hear about the blades breaking before the joint fails. I've killed several Buck lock backs. My Opinels have out lasted any of them.
Fun trick... undo the lock ring and batton with it. If you go nuts you may loosen the joint up a bit, but the lockring will take up the slack.
I've found them to be much tougher than their weight suggests and, as you've found, the blade profile is really amazing.