So in 10 months of Zwifting I have dropped 10kg. I have also gained strength and muscle endurance. BUT Zwift is based on w/kg. So when the Zwift peloton is moving at 2.8 w/kg, the old 96kg me needed to put out 270 watts to sustain 2.8w/kg, where as the new 86kg me only needs to put out 240 watts to maintain the group pace of 2.8w/kg.
I think weight has a lot to do with the performance level in this Zwift thread.