Well considering that the game has added content, higher native resolution, and a more stable fps than those consoles (as all last gen ports do on switch), 9 months is not really a lot of time.
Your Switch sales prediction was a bust, accept it. No need to grasp at staws trying to downplay the system. You are only hurting your own image.
That's the point. Doom on Switch and Wolfstain took almost the same time. While Diablo has been here since 2012 and run easier on PS3 and Xbox 360 that is slightly weaker the Switch.