rubiksoval hit it right. Outdoors you soft pedal more. Also, they chose those world's courses for a reason. UCI worlds. Not the weeknight group ride.
Also, check your proper weight in Zwift, your meter readout, etc....
Indoors, you need a great fan. Even then, it's not the same cooling effect. You'd essentially need to sit your trainer in a temperature controlled wind tunnel to get full cooling.
Even in a smart trainer in Zwift you may work more if not sucking wind in a group ride like outdoors. Then outdoors you're rested for the climbs.
Stick with it. It's fun. Zwift has some nasty % grades, etc...