“I don’t think it’s unfair to believe that if you use a rod with the correct rated tippet, it should never break during normal use (i.e., it should never break while fighting a fish, no matter how large). The tippet should fail long before the rod breaks.”
It may not be unfair to believe that, but it is not an accurate belief. Rods can and do break in normal use even when the correct rated tippet is used. First, you have to understand that tenkara in Japan is a method for catching 8-10" fish. That is the size fish the rods are designed to catch! Ten inch fish are not going to break your rod or your tippet. Who knows what Chinese copies of Japanese rods are designed for.
“No matter how large” is a concept that makes no sense with respect to tenkara fishing in Japan. Their fish don’t get large enough to break a rod. If the Japanese manufacturers thought their customers considered the tippet rating to be a guarantee rather than a suggestion, no rod would carry a tippet rating. As it is, Daiwa, Shimano and Tenryu do not give tippet ratings for their tenkara rods. I suspect I should take all the tippet ratings of my website.
Next time you watch a video of Japanese tenkara, try to find even one tree within range of their back cast. Here in the US, lots of rod breaks are caused by people trying to free a snag by whipping the rod. Also the unweighted wet flies used in Japan are rarely going to get snagged on the bottom. I am pretty sure that a fair number of broken rods here in the US are a direct result of snagging the bottom. The most dramatic rod failure I’m aware of was in a good quality Japanese rod. The angler, who shall remain anonymous, was pretty new to tenkara but was an experienced fly angler. I am certain that the rod was held low, like a fly rod, the weighted nymph caught a rock, and the angler set the hook as if there was a lot of heavy fly line stuck in the meniscus that had to be ripped out with an 8’ fly rod. Well, a 12’ tenkara rod moves a lot more line, which is a lot lighter and is not stuck in the water. The herculean hook set jammed the tip and second section - permanently - and broke two sections in the middle of the rod. The angler shared the story (although not the details) with a lot of people and no one could believe a rod could break “in four places” with “just” a hook set. That would not have happened in Japan, and no Japanese rod is designed to take that degree of what at least some American anglers think is “normal use.”
Quite a few tenkara anglers in the US have proven that you can catch larger fish than the Japanese would even imagine, but it takes skill and experience, and possibly a few broken rods, to understand how to fight a big fish and when you have to surrender in order to save your rod.
You are wise, though, in thinking that if you are not gentle on gear, you would be better served to choose robust rather than delicate.