The latest generation of cars is where the wheels have fallen off to some degree in terms of polarising styling and in certain parts of the model range (with the loss of RWD, manuals, DCTs etc)... and that is just because they are giving people what they say they want in focus groups or based on what their sales figures tell them LOL. At this stage we are lucky to be able to buy ICE cars at all let alone high performance ones.
Yes they made some strange decisions and it is totally fine to be happy with what you have, but it is a disease across car brands (for decades now) of current owners proclaiming "what they have is better and the peak of the brand" when something new comes out. I feel like we are confusing the polarising styling (which it really is more so in this generation than any other) with the other phenomenon that is almost 'normal' for car enthusiasts to fight over. The way everyone talks, you would think 99% of M2s and M3s would be sold with manuals and 50% of M5s would be manual... what do the numbers say? Almost nobody really wants them... then the next argument is that "enthusiasts don't have the money for them" rather than realising people given the choice and having experienced different things for themselves end up making different choices to people who have only imagined what it must be like to drive these things let alone own them.
1 series has progressively gotten better up until the last generation. You can long for certain things from the past but there is no getting around the progress up until the last F series cars.
The Z cars are a bit interesting in that you have to drive them and see which of them suits you - they are quite different. I feel like first gen Z4 owners have not driven the prior or current generation cars and assume they have gone backwards. I feel they are different enough that they will each appeal to different kinds of owners.
The G Series 3er is VERY much an upgrade over the F30 and if you think it isn't then you need your head checked. The only complaint is the cost that it comes at and that is really our economy and exchange rates to blame. The F30 showed some "legendary" cars some very interesting lessons and not just in a straight line.
G30 is also a huge upgrade from the F10 in terms of the tech inside, the styling of the G30 was not bad at all even at launch and didn't take 'getting used to'. Don't get me wrong, I love the E39... it is my favourite M5... but to say BMW peaked at that point with the 5 series (one of the most successful executive sedans globally in every generation) is a stretch. Even dynamically these cars (despite their size) really do perform well. F90 vs. my F10 inside (including quality of materials) is like it came from a totally different universe (not that the F10 was bad and I would still love to own an F10 again). There are things that you miss... I've written about some eg: missing some of the harshness of a DCT box... but there are other things that more than make up for this. eg: I had to google the dimensions because this car felt SO MUCH more nimble and smaller to drive and manoeuvre than my F10 did living with it for a while now- nope...
There are certainly cars that have indeed gone backwards or lost the plot in terms of positioning or where for instance they have 'skipped' a tier by virtue of size increases etc (eg a G20 vs E39 for instance) but the entire brand can't be painted with the same brush and if anything these are more outliers that are excellent and dogs than there are entire generations that can be written off.
You want to see a brand really trade on their former glory and reputation? Look at the entry level Mercs (C Class and below) - Renault engines, fake everything, screens everywhere, lazy design (and real regression in quality) yet they have had the same price hikes as BMW and Audi.