Just changing the fielding at the right time and bowl to a different plan can get a wicket! A new captain means new ideas, we wont know how good Root will be or if he has it as a captain until he captains the side.
It's easy to say change the field but frankly they could have had an extra couple of fielders on the pitch and done little better. When your first choice spinner is a batsman who has a dabble and the second guy is a trundler with no test record behind him you're doomed.
Cook could have been pressuring the selectors to get more spinners in and drop seamers but if Moeen and Rashid are the best we have maybe there simply isn't anyone else. You can't chuck some village bowler out there for the sake of it.