Apple recieved a fine for this and they claim it is not a practice they do anymore. That said with each release of IOS there is always degradation in performance because it has more features that take up more memory and processing power. The 8 uses an A11 Bionic chip and that is used in the 10 as well, 11's are on now to the A13.
So if the new update is geared towards the processing power of the A13, then yes unfortunately you will see degradation, but it shouldn't be significant.