It pays off in interviews to drill that stuff. If you want to be good at your job though, you just need to write a lot of code and understand design and architecture. The best book on this I read recently was “game programming patterns.” Ive had cause to use about a third of the patterns in the book in the last year alone, and my code base got simpler and easier to modify each time. Big payoff. Don’t read it start to finish though, use it as a resource for when you get stuck

http://gameprogrammingpatterns.com/