Color me skeptical that it is accurate that pipe is "missing" and is typical of all four pipes. It is true that damaging the pipe in two locations only 50m/165' apart would significantly slow repairs, either by subsea habitat welds or hauling ends to the surface. Completely severing and removing a section of pipe would make repairs faster as oppose to just blowing holes.
IF the estimate is correct and this damage is typical of all four pipes, it really points the finger at the US. Plenty of countries have the diving and ROV expertise but, AFAIK, only the US has the capacity to pull it off without detection — saturation divers and/or ROVs from a submarine.
It takes a LOT of bottom time and explosives to cause this much damage. A few divers on rebreathers hauling plastic explosives from a small boat couldn't get it done without detection.
My first question would be where was the
USS Jimmy Carter? This is pretty close to an admission.