I'm not sure what reference notes you're referring to.
10.2.1 was released 16 months after the 6s, so repeating "a year" over and over again undermines your point. Nothing we're discussing here affects anything advertised by Apple, so while you might be upset that there's something happening under the hood, claiming that they aren't delivering what they advertised is undermining your point.
Also you keep suggesting that this is happening with certainty to everyone you're addressing. I don't know if you know how to read a statistical distribution, and I'm not going to bother carefully integrating the probability densities, but it looks like maybe 20% of phones that submitted themselves to Geekbench were affected at all. There is selection bias in these results. People running Geekbench may be more likely to be power users, and power users may be more likely to deep cycle their batteries. Apple spec for warranty battery repair is 80% health after 500 charge/discharge cycles. 10.2.1 was released 486 days or so after the 6s, so if you charge your phone more than once a day, as you would almost certainly need to if you're regularly running up against the performance limits of your device, then you're likely past the warrantied life of the battery.
We don't have multidimensional data so all we can do is look at broad generalizations. There's a lot of inference happening from what we have, but I don't see anything that can be called "proof of failure". What I see is that right around the time we'd expect to see the first heavily used batteries start to degrade, Apple started mitigating the risk of random restarts. I don't see anything insidious in that, I see incremental improvement in reliability via a point update which is exactly how the release notes identified it.
Good design is giving the user the most from what they pay for. This throttling mechanism is doing that. Your alternative of maintaining identical performance for some arbitrary time period (measured by you in years, not battery cycles, so it's only loosely correlated to the actual hardware constraints) means denying the user the full capability of their hardware for that same time period.
Better batteries won't change this truth. All batteries degrade, so setting the maximum performance at the worst case, high usage, 1 year, cold temp performance level will always mean you get less performance out of the box.