You are applying some kind of moral value while we are talking about FFP. It is not EFP as in Ethical Fair play. If you complain about FFP, you don't take into consideration history otherwise Milan wouldn't have been in trouble being a much bigger club than MU.
FFP is a joke because Uefa treat it as some sort of PR term. They are not really commited to making FFP serious, a really tough rule meant to temper clubs having near unlimited spending power.
In any field, not just football, the rich have means to circumvent the rules, and it is something the powerful relentlessly find ways to do. Which is why rules have to be improved, so they can keep up with solutions constantly being found to trick them.
PSG must have skilled legal counselling, allowing them to find clever ways to make their dealings fit those half-assed FFP regulations. It's all on paper. Of course, in practice to whole idea of financial fair play, the meaning behind regulations, is being mocked and ridiculed systematically.