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.