At the time of the troubles, Romero was portrayed as the 'indispensable one' (protip, everyone can be replaced) and threw down a very public gauntlet with Daikatana. It was not well received. Which for many proved that Romero wasn't the secret sauce Carmack was. But like Jobs/Wozniak, Lennon/McCartney, Simon/Garfunkel and any of a doze pairs who often did things together that were often better than what either could do alone.