Bruce,
Even the best sword can not compensate for poor skill. I have seen a $3000 sword fail to cut through beach mats in the hands of a beginner, while the same sword cut through six tatami mats in the hands of an expert. We expect better results from students with superior swords. They should rely on technique rather than force. Cuts are expected to be cleaner and the angles more precise. I equate a cupped cut with a superior sword to failing to cut with a lesser sword. The superior sword can cut with almost no effort if proper technique is used. I personally cut with swords ranging from a remounted 26" WWII gunto to a 30 ½" modern Japanese sword made specifically for tamishigiri. Our targets range from beach mats to tatami wrapped around bamboo cores. I have cut both single tatami and bamboo with the gunto. I definitely prefer the feel of cutting with the superior sword. I can use all the help I can get when I cut big rolls of multiple tatami. The big sword can cleanly slice through a roll of four.