Didn't' read through this whole thread just throwing this out there. I was speaking to a shop that does a lot of a/c on cars and asked if they have seen this issue with BMW's with the poor a/c. While they said they hadn't specifically with BMW but had seen it on other brands. They suggested checking for refrigerant leaks.
The 1234YF refrigerant used now is a higher pressure system than the older 134a that was previously used. Higher pressure can lead to premature leaking thus weak a/c. I don't know if BMW is checking for leaks or if they diagnose the issue at all. I've been told the dealer in my town just dismisses customers saying its in spec.
But is seems that some have the issue and others do not. Perhaps it comes down to the refrigerant level.
On a side note I recently had to borrow a 2000 Nissan Altima for about a month while my truck was in repair. I was literally blown away how good the a/c was in that car. Ice cold and blew hard
We've definitely moved a step backward I think in newer cars.