Shirt sales are a vastly over-hyped source of revenue. I think when the last figures were announced, only two teams in the whole world sold more than 1 million shirts a year and even the likes of Arsenal and Chelsea barely sold 300-400k. We didn't even make it into the charts, with probably only around 200k sales worldwide. When you bear in mind that the manufacturer takes most of the profit rather than the team, I'd be surprised if clubs saw more than £10-15 of revenue per shirt, meaning perhaps £2-3m revenue tops. The club probably makes more money off stadium tours than shirts. Even signing the likes of Messi would probably not push our shirt revenue beyond £5m, largely because the vast majority of the shirts we would sell would be the Chinese sweatshop rip-offs sold in Asia from sources who give the club precisely zero cut of their profits.
That would unfortunately be where you are wrong. Dupont only argued that UEFA's Fair Play restrictions in their current form were unfair, and the court banned UEFA from making the restrictions tighter and said that they must in future work towards making them less restrictive. There is nothing in the ruling that says UEFA has to drop the break-even requirement, and they've made it quite clear that they intend to hang onto it - they are presumably planning on observing to the court that the introduction of the exemption system is proof of their intention to make FFPR less restrictive, and the rules against previous offenders benefiting are simply good administration. It would require a second challenge from Dupont to get rid of break-even entirely, and since the first court case took two years, that's probably a fair estimate of how long a second would require.