The answer to the first sentence is that Man City are new money and the elite don’t like new, they like the status quo, they want to ensure that the elite stays as the elite. Financial Fair Play wasn’t introduced to prevent clubs heading for disaster, it was introduced by the elite to make sure the small clubs remain just that, small. To stop clubs like Man City from smashing down the barriers and joining the party. Another club taking from the pot means less money for the already established elite.
During the noughties the four English champions league places (apart from one or two exceptions) were taken by Man Utd, Arsenal, Chelsea and Liverpool. Then a decade ago Man City’s billions came into play and those four became scared that one would be missing out on champions league revenue (after all everyone knows 5 won’t go into 4) and that had to be protected. Hence FFP was created. Another club also now competing for the few genuine world class players also makes it harder for those that have been pushed out to now attract those players. How many world class players now want to join Arsenal, or even to a lesser extent Man Utd. The mediocrity that has now come at these clubs that have suddenly missed out on a couple of seasons of champions league revenue is partly why clubs like Leicester and Wolves are now forcing their way in and creating competition to a league that was dominated by the big few.