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

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

The big tangled enterprise codebases I've dealt with had absolute metric tons of undocumented domain and company-specific "tribal" knowledge baked into them.

Technical prowess helps, obviously. But is not enough on its own.

Domain knowledge helps too, obviously. But even combined with technical prowess it is still typically not enough because of all the embedded tribal knowledge.