I did a zwift race, one of the tour de zwift catch up sessions. Because it was a catch up session, there weren’t to many people and I placed 3rd. From the gun, the winner time trialed off the front, the second placer tried to bridge the gap, but didnt make it. I time trialed off the front of the small group and rode the race on my own. So, 3 riders, no real drafting happening because we all rode separately. The course was sand and seqouers (sp?) so not really too many hills.
Both me and second place averaged about 250 watts, the winner, who beat second place by 20 seconds, averaged a bit over 200 watts.
Watts/kilogram is an important factor in Zwift. The winner was probably a much lighter rider than you, and therefore had a higher w/kg. This will make the most difference on climbs. In the flats, absolute power is a bigger factor than w/kg.
For example, a friend of mine is a little, skinny climber-type. At 260w, his w/kg is about 4. For me, 260w is less than 3 w/kg. I would have to put out over 360w to hang with him when the road goes up.