The rich, established elite who are there on merit now mostly got there because at one time they were the teams spending the massive sums of money to build stadiums and bring star players when there were no rules. That's my point, there's been an arbitrary cut off point where it was okay to do that in the past and make yourself successful but now no clubs are allowed to do that and hurt them. It's hypocritical beyond belief. Horrible concept.
I think the biggest concern was from overseas owners using clubs as an opportunity to laundry their cash, or paint a new brand of their regime, whilst coming in with the financial support of a nation.
It's one thing to have a club from a big city, owned by people from said country, building their success over decades, even if it includes over spending others. The big clubs across Europe did not become so in a decade. City, Chelsea, and PSG have tried to to so in less than a decade, and along the way inflated the market for everyone else. Additionally, even if clubs were overspending other clubs, the issue isn't about equality or an American sort of system where clubs are "equal", obviously heritage and history offer a valuet that is difficult to compete with, it's the access to almost limitless funds (the funds of a nation) that is injected into clubs at a rate never, ever, seen before.
FFP is not about equality amongst teams, it's about protecting current teams and leagues from current, and potential, owners with no concern over finances, changing the landscape of the game. City, PSG, and Chelsea in their time, have massively affected the finances of teams all over Europe simply be inflating salaries and transfer fees. That is the threat to the game. Having a group of elite teams in each league with an historic advantage that cannot be easily overcome in the short term, can actually make the league more attractive for viewers. It seems viewers want to follow leagues where "big clubs or teams" challenge each other in history, rather than having a circle of 18 clubs that can each win a trophy in any given season. Obviously, supporters of those respective teams feel different.
Having said that, having a league where only 1-2 team dominates also kills the game. Honestly, I don't think it gets any better than the Premier League where a group of 6 or so teams have picked up the trophy over the past 30 years bar one exception. Possibly, that's as good as it gets today where football has benefited from, and built a synergy, with business.