Oh Jeff, I think you have some image of a group of eggheads with degrees on their office wall present their carefully calculated specs to the manufacturing department, and a product is just made that way for the company without any other input or weighting. And if anyone questions the authority of the engineers' decision, that they, being alpha-male types and secure in their own mental superiority, will confidently defend their position having already considered what is best for the end user of the product.
Maybe initially it was, which is why they started with a 5 rivet tip. It seems like a solid standard. Oregon uses a 5 rivet tip on their RSN bars. Stihl uses 5 and 6 rivets on their E and ES bars. Canon superbar uses 6 rivets. GB uses 6 rivets (on the Australian made CN40 and PowerTip +, and Pro Top lines). SugiHara uses 5 rivets on their RSN bars. So does Laser, Frostbite, Forrester, Windsor... Carlton/Sandvik uses either 5 or 6 rivets. GB did move to 4-rivet tips on their lighter-weight Arbor Tech and Arbor Pro bars. And many laminated bars use 4-rivet tips... So maybe you can 'get by' with a 4 rivet tip. There is some user data out in the field on how those products last.
And maybe at the Tsumura company, the CEO wanted to buy a new house and wished his company sold more product, and the accounting department said they could increase shareholder profits if they lowered overhead. And the advertising department did a survey and said people had trouble justifying or differentiating the high price product next to SugiHara. And the sales department said they really weren't selling that many replacement bar tips, because the customer was wearing out the rails before the tips.. and so one day the engineers were told by upper management that the CFO would like to change the product to use less parts, and be made faster. Cheaper.
So the engineer is now asked not if a 5 rivet tip is better than a 4 rivet tip, but if a 4 rivet tip will last at least half as long? And the engineers say that most of the strain on the bearing in the tip comes from lateral force when plunge/bore cutting, but during normal felling, limbing and bucking there is little more additional stress on the bearing, and a 4 rivet tip should be "sufficient enough" in those conditions. So the CFO asks the marketing department about the demographic they are targeting, does a quick calculation (guess) that most of their customers using a chainsaw with one of their lightweight bars don't often push the bar into a tree during felling, and tells the engineer to design a version of the bar with 4 rivets and send it down to the manufacturing floor. The sole engineer in the engineering department, who actually has no support team and is not actually an alpha-male, knows who signs his checks, so he does.
Now, who knows if that story is true... maybe the engineers were asked to make the product even better somehow and changed the metallurgy of the rivets and changed suppliers, started using some fancy new hardening process on those 4 rivets making them each 125% stronger than a normal rivet, so they can get away with fewer of them?
Maybe.
You keep on using your Tsumura lightweight bars, Jeff. I'm sure you'll be fine. But as for your ideas that engineers are dictating the best decisions all the time, you're just being naive.