Voyager's ratings were never as bad that they only got 1/20th of what TNG got! Edit- oh you posted. Well that 1.9 was that "special extra episode" Juggernaut so that doesn't count! Their lowest ever rated regular episode was "Shattered" with a 2.8 rating compared to the tenth episode of TNG's 7th season which got a 12.1...so yeah pretty big drop off, although the number of households/viewers that a nielsen point represent does change with time so its not a completely 100% fair comparison. Although obviously a huge drop off of around 75%.
As for the impact Seven of Nine had on the ratings, very short lasting. Claims that the show was on the verge of being canceled and that she saved it are just flat out wrong.