The debate that cemented Tanenbaum as a smug clown in my mind since '92, his poor students!
You need to understand the theory and the design if you want to design something that will last for generations without becoming a massive pain to maintain.
Linux now is a massive pain to maintain, but loads of multi-billion-dollar companies are propping it up.
If something only keeps working because thousands of people are paid to labour night and day to keep it working via hundreds of MB of patches a day, that is not a demo of good design.