I’ve seen that fact in a number of presentations on the Military channel. the rubble was a better high ground than the abbey itself. but who knew. all the allies knew was that the Germans had it and we needed to take it....
the allies did amphibious end runs around German lines on the peninsula though...like Anzio....but I do believe the mountainous spine of Italy was not completely defeated till operation overlord when the focus was on northern france and the Germans sent troops up that way...as did the allies.
The other factor in Italy is the weather, which is hampering air operations and making the life of the infantryman an awful mess. Once summer comes with warm, dry weather, the allies can operate freely in the air, and mobility is restored to the ground units. Of course, Italy is a low priority for the Germans behind France and Russia. While they are not getting many replacements, the Germans did not feel the need to pull units out of Italy wholesale, as the offensive that broke the Gustav Line began before D-Day and also before the Soviet summer offensives.
I would say that while the Germans are making good use of the terrain, it’s really the weather that is keeping the Allies in check.
The Allies in the Mediterranean did not have a lot of good options for offensive action after Sicily. Churchill was pushing for more dangerous adventures in Greece and the Balkans.