It's also bizarre when people see "it can't be legal for UEFA to tell a club that it can't use its own assets". As though, if it ever got to a real court, FFP would instantly be destroyed.
That's just people trying to sound legalistic without any knowledge of real world regulation. Freedom of contract and property isn't absolute.
Competition law exists, and it allows you do all sorts of things in the interests of market competition and consumer welfare. You can make all sorts of demands on companies.
You can nullifyhuge contracts and partnerships, you can force companies to raise or lower prices.You can deny companies the right to merge - you can even command a company to break off a division as a separate company if you feel it threatens competitive balance. You can command Google not to prioritise its own pages on its own search engine - that's how specific it can get.
A private club of companies, which is what UEFA essentially is, asking its members to maintain a certain degree of financial stability is nothing in comparison.