Not much I agree with here I'm afraid. UEFA did not have to act on the leaked emails. If that is all they have they are a weak basis for a charge and a finding. Secondly, they could easily have said, "these matters were investigated in 2014, we believed City inflated sponsorship revenue and entered into a settlement agreement and settlement regime where we monitored them closely for 2 more years. Accordingly, these matters are now closed. If we find evidence that this occurred in the periods now under review we will take action." That would have been the end of it.
City could have accepted a ban and still can. Indeed if they thought they were going to fail at CAS they would be offering all sorts to get the ban down to one year. A 2 year ban is not double a one year ban - even more so following Covid. To miss the 2020/21 CL is no big deal especially if a settlement blocks any PL consequences. Going to CAS loses control of the articulation of the breach. It is risky.
So we could get a reduced ban from CAS but still be in a very poor position with the PL.
As I have said over and over, the procedural failings of UEFA are not now relevant to CAS. CAS will cure them - the case will be heard on its merits both in law (ie the rules of UEFA and Swiss law where relevant) and in the substantive matters. Any comments CAS makes about UEFA whilst finding against City would be a pyrrhic victory.