If I were to summarise, I think the PL now think they are finished with this. Certain parts of the rules were unlawful, but the rest, they say, continued in place. The new rules correct the unlawful parts and so they think they can now re-assess the Etihad deal under the adjusted rule set which, as the unlawful parts didn't affect the original assessments particularly, they can come to the same conclusion that it is still overvalued. This assumes the PL's position on the old rules is confirmed by the tribunal.
Assuming that City started this whole rigmarole to get the Etihad deal through, then I think City are confident in their legal position that the rules are still null and void. In this case the Etihad deal sails through unchecked and the recently approved rules become null and void, and a whole new ruleset will have to be approved later. As a result, the club will, in the words of the great bard, have won "the greatest victory since the Winchester flower arranging team beat Harrow by 12 sore bottoms to 1!".
But why did the correspondence between the two parties get so vitriolic for a vote that is actually pretty irrelevant as I doubt it changes the tribunal's forthcoming judgment at all.
There is still a nagging question in the back of my mind about whether City may have bigger fish to fry. If they are successful in voiding the APT rules for the treatment of shareholder loans, then maybe they can challenge the lawfulness of FFP/PSR for the same reason (this could be the reason why the club seemed to have accepted, or at least didn't oppose strongly, that the APT rules were a vital part of FFP - something that always surprised me). And if FFP/PSR is null and void since inception it gives the PL an enormous headache for many reasons. Not the least of which is that FFP wouldn't have existed through 2018, and the 115 allegations would fall apart. For those saying they would still be serious allegations, consider this: without FFP, there would be no sporting advantage to the club even if all the 115 allegations were proven. They would only be administrative breaches and breaches of good faith and so would only be subject to a fine.
That would explain the aggression shown by each of the two sides, trying to protect their positions in the bigger picture.
I am reasonably sure paragraphs one and two are pretty accurate but the rest is purely speculative, of course. Please shoot it down if you think it's complete bollocks. I have no problem being told I am talking bollocks, which is just as well. It happens a lot :)