Anecdotal. But I haven't spent $5k in repairs to my 17 year old bmw in the 10 years I've owned it. I do budget for $1k a year though.
The electric water water pump alone was $2,000.00. $1,200.00 in parts and $800.00 in labor. This is basically a “maintenance” item. The car has less than 100k miles and is on the third pump.
The reality is BMWs just have a lot of stuff on them and so it is a numbers game. Things are going to break. Cars are a hostile environment. This is compounded by the fact that it is a BMW. I expect everything to work. If it was a used Corolla I may not complain as much about the seat mechanism not working perfectly every time.
Additionally BMW also expects the car to work perfectly and the car is eager to tell you any time something is abnormal. This creates something of an illusion of unreliability. An old Toyota also has a lot of problems, you just don't notice until you go looking.
And finally, dealers are predatory. They take advantage of the reputation of BMWs as expensive unreliable cars and sell unnecessary services, which perpetuates the expensive/unreliable reputation.
I'm also lucky enough to be trained in vehicle maintenance; The only service I've had done by professionally were recalls and when I didn't have garage available to do the expansion tank (and Pep Boys didn't have a supply chain, so I got my choice in parts)
The electric pump is great from a performance/efficiency perspective because the car can make choices about coolant temp irrespective of engine speed. It's a horrible device from a reliability perspective though. I have already been stranded by it once.
My turbos are "fine". But I know they will fail in the next 30k miles. In talking to my mechanic the prices fluctuate quite a bit, so I am going to start keeping an eye out and just buy a pair to have on hand when mine finally let go.