Sandy Petersen shared his opinion back in September. He wrote on Twitter that Doom II was done so that developers could get “quick money” and use assets from the first part. In addition, this way the designers could do something while they were working on Quake.
On October 10, John Romero commented on the tweet. He disagreed with Petersen and stressed that Doom II was the same full—fledged retail continuation of Doom as Spear of Destiny for Wolfenstein 3D.