John Romero was making shareware games for years before he met John Carmack. He wrote the level editors, much gameplay code, created many levels for, and significantly contributed to the game design of all the id games from Commander Keen to Quake. His absence is arguably a big part of why most of the later id games just aren't as fun as Doom. Daikatana bombed for a lot of reasons (zero experience as a manager, dotcom-era ridiculousness in hype and project scope, infamously horrible marketing campaign that he had no part in, etc), but not because John Romero was an incompetent programmer or game designer.
If you have the time, watch this series in which John Romero and (Bioshock level designer and apparent Doom fanboy) Jean-Paul LeBreton play through the first episode of Doom and analyze its level design in depth:
Thanks for linking to that video, it was fun to watch. I've looked at the 90s' id games differently ever since I read Masters of Doom 10 years ago (due for a re-read soon) - learning their history made me appreciate those games on a whole new level. Their story was a very big inspiration and motivation boost for my own modest projects.