Zwift can be harder than riding outside, there are no natural stops, such as traffic lights or busy intersections. The drafting effects in Zwift are much less than in real life. You’ll have to pedal harder in the draft than you would outside.
You can coast down a few steep descents in Zwift, but the overall effort of riding and racing on Zwift will always be harder than riding outside. The best part about this is you’ll get fitter faster by pushing yourself to new levels on Zwift.