It's not a "myth" and I don't think it's far from the truth. There is certainly verified data (Consumer Reports, JD Powers, and many car magazines, etc..) which report that the main issues with modern German autos are electronic bugs. I think there's a reason that Japanese autos overall have a record of higher reliability.
I much prefer German autos for the sheer pleasure of driving them. But they do seem to need more attention and quirky electronic issues are not uncommon. That you have had an issue with a Mitsubishi doesn't mean that it's all a myth. It means that Mitsubishi isn't up to standards of other Japanese makers (and that is pretty well known if you check Mitsubishi reliability over the years. It's not a brand I'd personally recommend as an example of Japanese build quality.) But still, the statistics do place Japanese built cars as more reliable in general compared to US or European made autos. Pool all the data and I think that's why the general consensus is that Japanese cars are the most reliable on average.
That all said, my 18 year-old German car has been incredibly reliable. But then again it's also not laden down with lots of electronics (except for the immobilizer module that is a PITA and something Porsche should have never implemented 😡)
I'll also say that modern German cars are getting a lot better now than in the past when they were first implementing lots of electronics. And I feel that it's the same with Leica. They are relatively new to the game of digital but are definitely getting better with each new model.