Kind of amazing. I’ve poked around that sukekai website many times, and I frequently find something I had not found before. I don’t recall seeing that particular webpage before. I liked the proverbs about broken rods.
As for the topic of this thread. Which perhaps should be durability vs flex vs weight vs cost.
Yes I think rod design is a delicate balance of trade offs made during the process of rod design and prototype testing.
You can read about some of the thought process during rod design in some of the articles in the list on the Shimano keiryu development website [ シマノ渓流 開発・奮闘・記, That translates something like - Shimano keiryu development struggle record ]
So yeah, it’s a struggle to balance design choices to find the sweet spot for a rod that’s not so heavy, but super durable people wouldn’t buy it. They search for a design that is lighter yet durable enough that it wouldn’t soon develop a reputation for being fragile. But still also has desirable flex and thin enough profile to have low wind resistance. All vs cost of materials and production.
Some of the desired characteristics are more easily obtained by using expensive raw materials, but at the risk of making a rod so expensive many people wouldn’t purchase it. However, I think sometimes rod manufacturers will also make a few rod models that are very specialized, aimed at experienced anglers, who are not clumsy in how they handle or use the rods, who want a rod with the primary features of; low weight, desired flex, and thin profile, and they will tolerate high cost and low durability to get it.
[ I see a parallel here among the ultra-light backpackers. Low weight cost money. An 8 x 10 cuben fiber tarp might cost 2 ~3 x as much as the same size tarp made of sil-nylon, but weight half as much. They are the guys who end up with ultra-light weight camping gear, and an ultra-light weight bank account too. Some of their UL gear choices are expensive, and durable. Other UL gear is expensive, very light, but not as durable as heavier less expensive choices]