MYF Tower Controller reported low wing single engine aircraft departure deviated into parallel Runway traffic resulted in a NMAC.

Narrative

Aircraft X departed Runway 28R for a right down departure. The aircraft drifted to the south into the departure path of Runway 28 left; which had Aircraft Y departing. Aircraft X was reported to be right on top of the Aircraft Y by 100ft; radar display replay confirms altitudes. Aircraft Y reported it to Local Control 1; which told Local Control 2; at this point Aircraft X was in the crosswind turn away from Aircraft Y. Even when told about the situation I could not see both aircraft due to the Window Shades blocking my view; they were pulled half way down. When the shades are like this we can't see the top half clearly; but others like it; because it blocks the sun. I personally cannot stand the way we do our shades; but I'm in the minority and the majority rule. I was also busy looking at the arrivals during the event to ensure separation between arrivals. With the amount of volume that we have; I recommend implementing a local assist position to help get more eyes out the window to prevent these types of situations. Our local assist position has been waiting for approval for years.