The survey showed that iOS 11 reduced the speed of the previously released smartphones iPhone
A survey conducted by the resource Phone Arena, proved previously suggested: iOS 11 actually lowered the speed of the previously released iPhones including the iPhone 7.
The survey polled more than 3,300 people, 31% of whom said that their smartphones have begun to greatly slow down when working after installing iOS 11. Another quarter of respondents agreed with the fact that the phone began to work slowly.
Only 22.85 percent of the people who took part in the survey said that their smartphones are working after the upgrade as well as before. Loss of 21.16% of respondents were Android users.
I should add that iOS 11.1, according to reports on the forums, improved the situation with slowdown on some smartphones.