Under FFP the source of funds IS important, if they're disguised owner investment. The emails being hacked led UEFA to suspect that was the case but even if it was, that's allowable if the sponsor is classed as a related party and the revenue from that sponsorship is in line with what a non-related party would pay.
If I recall correctly, UEFA tried to argue that all the Abu Dhabi companies were related parties but this never really got resolved as it made little difference at the time. We didn't agree about related parties as we've never declared them as such in our accounts (which we are required to do when there are transactions with related parties) but we did agree not to increase a couple of what were described as second-tier sponsorships (Aabar and another).
Also, if I recall correctly, UEFA conceded that the Etihad sponsorship was in line with market value so however it was funded was irrelevant (according to their own). Now they're claiming there was disguised owner investment yet, in their 2014 investigation, that would have been OK according to their own classification of Etihad as a related party.
There's another thing that might be very relevant to our defence. Almost as soon as the ink was dry on the cheque paying our fine and it'd cleared in UEFA's account, they changed the FFP rules to allow a period of owner investment that might normally breach FFP rules, in the case of a change of ownership. I read about a case brought to CAS involving the US NASL and FIFA. This involved a club dropping out of the NASL but the club that won the second tier league weren't promoted. The appellant club claimed that FIFA rules mandated promotion and relegation and that the NASL had failed to implement that. CAS ruled that it wasn't necessarily what FIFA said but what they meant and how they applied the rule, and it would place more reliance on contemporaneous action than historic ones. FIFA hadn't enforced the rule on leagues that, when the rule was introduced, didn't have it and if I read it correctly, the ruling said that it clearly wasn't their intention to enforce it on leagues that didn't have it, whatever the rule actually said.
I do wonder if we could bring a case against UEFA claiming that they pursued us for breaching FFP yet their more contemporaneous intention was to allow a period of owner investment and that the main reason we failed in 2024 was that we accelerated investment before FFP came in whereas now we would have a period of grace. The real investment only started in 2009 and therefore the 4 year period of grace allowed under the current FFP rules would have ended in 2013, which is the period we've been punished for.