I disagree with that list. None of those cars are terrible if you do your research, can wrench yourself at least a bit, and buy an example with your eyes wide open. If you buy an example at a used car lot, and expect to bring it to Jose gas station and garage down the street your in for a rude awakening and the ownership experience will be very painful.
I have helped do a T belt on a 328, its about $1k worth of parts and if your mechanically inclined you can do it yourself. When I eventually get my 355 I plan on doing just about all services myself, but I'll have access to a heated garage with a lift etc.
The 6.3 again if kept in good order is not terrible, but there are some very expensive failure points that can be avoided. A perfect example is not using the Mercedes hydraulic oil that operates everything in that car. From the windows to the sunroof and seat adjustments! If you use say regular ATF trying to pinch a few bucks that's a $25k mistake because all the seals will start leaking.
People that buy cars like this need to remember, that just because you can buy them cheap now they are still complicated high end vehicles. So don't expect Ford Focus operating costs, expect them to be more in line with a modern $200k-$500k car, which is inflation adjusted what they cost new. How much does a carbon/carbon brake job cost on a new Bentley?
The flip side is that in general with the active owners clubs now you can get stuff aftermarket or rebuilt vs new. Ferrari, Jag, RR, and Mercedes have very active owners clubs full of guys figuring out how to keep these old cars on the road. A lot of parts on those cars can be rebuilt for a fraction of what new costs. Like the seat switch's on just about all Mercedes, even newer electric ones.