I know first-hand that Mercedes are quite user-serviceable, as I do most all of the service (ex-tire replacement, ex-exhaust) on all our cars.

Factory basic service information is not only easily available, it's free (at least in the US: they make you provide a US CC every 365 days for online access, so it might be MB-USA funding it, but the card is not charged). Parts are readily available aftermarket, from OE and non-OE suppliers. There's also several well-respected third party shops within a few miles of here.

I don't drive a BMW, but I know of two excellent (but not cheap) third party shops nearby.

Yes, some systems are computer-augmented for service, and require a beyond-OBD2 level of software, but that software is available (and a couple thousand dollars, a lot for an individual, but nothing compared to the rest of the tools a shop has to have).

I am quite happy with the supportability MB provides, and probably wouldn't drive one if your statement above matched my experience.

Side note: it's a pleasure to work on MB: very few "one time" fasteners (like those plastic Christmas tree push things, or ridiculously fragile/undersized plastic latches). Thing that you need to take apart are designed to be taken apart and put back together many times without damage or leaving ill-fitting parts afterward. You really notice the difference when servicing someone else's other brand, price-optimized car.

Good for you that you can do it yourself. We don't have the time to do that and we rely on good workshops. Here in germany non-contract workshops cannot get access to the necessary tools and software. They could hack it, but thats against the law! Most mechanics also lack the abilities to handle analysis software.

As a bottom line, workshops that can service cars with new production date vanish.

What you say is indeed the solution that came into my mind: buy a cool oldtimer (I especially like the Porsche 911 from the late 70s/early 80s) and buy a new house with a large garage. Tools are available already.