Most debts are manageable, and some clubs (like ours, Arsenal) are forced into debts for the long term growth.
If we need built a brand new stadium we would have struggled to compete against mighty Man United and their spendings, as well as other top clubs around Europe.
One of the major criticisms of FFP is the possibility of solidifying the so-called big clubs which generate largest revenue and profits, and can consequently spend more money on transfers. See Bayern Munich. They'll be a force for a long long time. They are self sufficient. Make huge sums in revenue, and have massive commercial deals. They aren't in much debt too. They're pretty safe.
I don't know if FFP will make it a more level playing field, but I hope it goes some way in clubs just buying their way out of a troubled season, and instead, start using their heads and tactics.