Wouldn't you also get more hardware errors, causing e.g. sudden kernel panics and stuff like that? And wouldn't that damage the brand more than the speed improvement is worth?

I don't think that's a fair representation of what's happening though. The reality is that running it at 110% (for whatever that means) is using a new battery at its maximum discharge rate. As the battery ages, its maximum discharge rate decreases, and would have whether run at 110% or 90%. You need to go way out of spec to prematurely age batteries by discharging too fast. They age mostly by being exposed to high temperatures, stored fully charged, and by being fully discharged (partial charge cycles are better). Artificially limiting performance to the post-degradation level can be seen as wasteful, can it not?

Now the way Apple handled it, silently, throttling performance without a configuration option is interesting. I think the benchmarks may not be truly representative of what is happening, and it's probably closer to a TDP limit on the CPU where it runs real fast until it realizes it can't then it ... doesn't. That comes across as maximally efficient in real life but slow in benchmarks.

This is all in the marketing. Either you can look at it as "iPhone find a way to squeeze every last bit of battery life out of both new and old devices" or you can look at it as "my phone slows down over time" -- the reality of the chemistry of lithium ion devices.

IMO this should be handled with a configuration switch and a notification when performance starts to become limited, though how many would be totally confused by this? That hundreds of millions of users took years to notice should be an indication this whole thing worked pretty well IMO.

Hmm, just a bit skeptical about that. I'm pretty sure that peak "110%" usage rarely happens throughout the day; Maybe during video playback or gaming.

This is especially true since the iPhone 7, with its two low power cores who's entire purpose is to extend battery life.