The tie down rings are more substantial than they look. I had to remove one of the rear quarter trim panels to replace a 3rd row shoulder belt and retractor (due to a dog getting out of a non-robust kennel and chewing the belt in two) and noticed that the tie downs are attached to pretty beefy metal brackets back to the body structure. As you can see from the link above. The master won the kennel robustness competition with the dog.
As a result I use them to hold my truck vault/kennel assembly in place (shown on the media page above). While gravity does a good job of keeping everything in place, if you grab some air with the rear wheels, the assembly (estimated 350#+ fully loaded) would levitate and slam if not secured to the vehicle. Having been through a few of those cycles, the tie downs haven't budged in any way.
I used double lash straps through the tie downs tightened over the top of the vault, holding it securely in place.