I know this is the general train of thought on this and I do understand the mentality but I'm not sure I totally agree. The comparison is always a car that magically teleports itself to the motorway and never drives in town being compared to a car with the driver profile of a minicab. The reality is that even a car that clocks up big miles still has to start and end its journey somewhere, probably including a chunk of town driving. The main difference is that it also spends the day doing a motorway stint on top of that.
Where it is offset is that the car is still relatively new and I'm very much of the opinion that it is a combination of age and mileage that wears away at a car and at this price point it does seem like a bit of a no brainer as long as you go in with your eyes open.
The proof is in the eating as such, this particular 520d would be hard pressed to be described as a 100k miler from how it drives, as would have been the 260k e39 I had a few years back, of course a car will cover short trips to get to & from said motorway, but, ultimately, a high mileage in a short ish space of time will always be less taxing on the driveline than a similar figure over a longer period.
A car thats been used as a minicab soon stands out, it'll have all the wear points of such use, as an example, this 520d dosen't, its drivers seat shows slight (and I do mean slight) sagging, the rest of the seats are unmarked and uncreased as you'd perhaps expect from a car thats predominantly carried one guy from business meeting to business meeting day in, day out.
I have a mate who works selling used trucks, he always prices high mileage sub 3 year old examples higher than vastly lower mileage ones of equivalent age, the reason is the lower mileage useage tends to fit with a higher wear & tear useage cycle, the market reflects this, he has little issue selling the higher mileage examples where the others he tends to punt straight to auction as he knows they tend to be the ones with warranty claims further down the line...
Edit, to clarify, the truck market - unlike the car market- is far more focused on the likely life a vehicle has lead, it generally stands to reason that a lower mileage vehicle will have far more general wear and tear - on the driveline especially - than one that’s covered a higher mileage in a similar period of time, which is why the above tends to be the case.
I know it myself through the many trucks I’ve driven over the years, you can almost guarantee a truck say 3 years old with 400k KM on the clock will drive far better than one with half that mileage, predominantly because one has racked up the miles on motorways and A roads, the other has accrued it on local stop start use which takes far more from the vehicle.