It's also worthwhile to remember where the team honed their craft, as was also mentioned in this session: The early id team worked for a publisher called Softdisk that provided a game subscription where customers received a new game every month. This was basically a way to iterate on the practice and process of game development in one month cycles. The shareware relase of Doom had four months of development, which sounds crazy short by today's standards, but for them it was unusual to have so much time.
There's several talks on Youtube by John Romero where he tells the story of the early id software, e.g. https://www.youtube.com/watch?v=E2MIpi8pIvY