Picatinny offers a more repeatable zero with less room for error than M-LOK at the cost of weight, bulk, and feel in the opinion of some. The test equipment was failing, not the actual Picatinny shearing or damage to the 1913 rail IIRC so I would hesitate to use that information to reach a conclusion about the robustness of Picatinny. 1913 has more than proven its robustness and zero retention with all manner of optics and lasers over the years, with some methods of attaching to the Picatinny rail being far more effective than others.
I would argue that even if the handguard or rail itself isn't damaged, the fact that the mount fails says something about the system itself. For sure, 1913 can't suffer from the slippage issue that M-LOK can, but taken as an entire system, 1913 isn't necessarily a clear winner from a raw strength perspective.
But to the original point, yes, full quad rail handguards aren't really relevant anymore going forward, IMO, which is not to say that they don't work, just that there are better options overall, when you have to include issues like cost and ease of manufacturing. For general issue service rifles, having segments of 1913 at the end of the handguards certainly has some merit, simply due to logistical issues of attachments, but a full-on cheese grater probably isn't needed.
