it was outside an race, just a group ride. I did supertuck being alone on the descent.
Id forgotten that about Zwift slowing riders on non race events. Odd they would do that
Yeah I think the fact one descent was in a race and one wasn't will explain the big difference is speed as Michael said - Zwift actually apply a bit of braking when descending while not pedalling when you're not in a race - so a descent like that in a race will be MUCH faster. In a race the supertuck is equivalent to the aero power-up in terms of gains.
Zwift say they don't give the same advantage outside of racing because they don't want to incentivise you to stop pedalling when free riding, and it also makes it easier for groups to stay together or catch each other up in group rides if some inadvertently go off the front.