I don't think it's horrible or unusable. I just disagree with them switching it back because it feels better to me on iOS 10 on my 7. I don't think it's necessarily planned obsolescence either. Just a dumb design decision to change it back. At this point I highly doubt they will change it back. And there won't be many more years with iPhones that have home buttons so it doesn't really matter anyways. iOS 10 on the iPhone 7/7+ will always be reguarded as the fastest responding iOS version for the capacitive home button iPhones. And I will stay there. No point in updating to lose any responsiveness from my iPhone no matter how small.
I agree with most of what you say. We don't know why they decided to unify at this point, but planned obsolescence is a wacky theory, given it applies to month old phones.
It's certainly your choice to remain on 10 if you don't see value in it. I fully expect overall system performance to be similar/the same as 10.3.3 on all supported devices, and certainly the 7 as iOS 11 is optimized over time though. 11.1 is getting pretty near to that already.