Descending sucks if you're really light as well; at 145 lbs I have to descend at threshold to keep up.
The more I Zwift the less I do Zwift racing; asking myself the question, 'what does this do to help me win a real race?' and the answer is not much. My power profile just doesn't lend itself to a great experience (I'm usually stuck between the A's and B's alone) and other things are more optimal (workouts). If I had a good 1-2 minute it would be different but I dont.
I do think the 100k group rides are a great workout; 2 1/2 hours at over z3 is a great workout.