I think the working load limit of most chain is set around 1/3rd of breaking strength, so those chains would probably have a breaking strength roughly similar to the strap.
Also, I think some strap manufacturers list their "breaking strength" as the webbing alone, ignoring the weak points that are where the webbing bends tightly around a hook at either end. I say this because I've noticed the same rating listed on the same straps, in both hook end and loop end. The stitching could also be a weak area, but I suspect most good brands put enough overlap there to ensure the stitching at least exceeds the strap strength.
Did your strap fail in the middle or where it goes thru the hook? If in the middle, was there prior damage in that area?