I'm not doubting your story, but this is not the norm in my experience.

    It’s certainly true that it helped I was 
    familiar with the domain

Technical prowess and domain knowledge are excellent assets, obviously, but in my experience they're often not enough.

The big tangled enterprise codebases I've dealt with (insurance companies, fintech, construction, etc) involved absolute metric tons of undocumented domain knowledge and lots of company-specific "tribal knowledge." Some tribal knowledge was embedded in the code in undocumented or semi-documented form, and much existed outside the codebase entirely... all kinds of custom infrastructure, etc.

I don't care how sharp and domain-familiar a team is. That sort of situation is not easily tameable.