>> and then to spread the legs extra wide when shooting birds at eye level;
Moy, I would be VERY careful trying to do that. With any tripod, as you reduce the leg angle you dramatically increase the stress on the tripod mount connection to the legs, the leg collars, and the CF tubing. The entire assembly is strongest with the leg locks in the "normal" (highest height) position.
For example, if you fully extend a tripod (without a payload) and set the leg angles to put the tripod as low as possible, and then *gently* press down on the mount, you will see everything flex. I would never shoot that way- this is just a visualization exercise to be done with great care and gentleness.
I only increase the leg angles when the tripod is fully retracted or nearly so, so that I can use it in a seated or lying down position at a comfortable height. And especially when fully splayed out I am very careful not to put unnecessary downward stress on the tripod. My 500/4 is enough stress for that position.
Your source is suggesting something in between, with a Gitzo XLS or one of the new Giant models. The amount of stress would depend on how far you spread the legs and I have bo idea where the (literal) breaking point is, and that would depend on the payload and how you used it and "abused" it while going about your business.
I have a suspicion that the few reports you see of broken Gitzo legs or mounts are do to overstressing the mounts with the legs splayed, or use in deep snow, which is apparently even worse if not done correctly.