Zwift is good for training when you can't get out. I use it quite alot now I don't cycle to work. It's purpose is to keep me fit without being completely bored. It allows my to enjoy my MTB rides at weekends and has got me fit enough to get round the Black Route at Llandegla without walking the hills - cleared them all last month, first time I'd done that since breaking my back. My overall climbing has improved as well through using Zwift and pushing hard on races/training events.
I don't get bothered where I place - it's only worthwhile if you look at your times as that's the constant - you can track your progress as the next time you do a particular segment in Zwift, it's exactly the same as every other time you did it, so it's a good gauge of your fitness/wellness.
In the real world, a single climbs can be very different depending upon the weather. This time at Llandegla, I got up the 3 mile climb the quickest I've done before, despite the howling headwind. Next time I might smash it completely if there is a tail wind, or indeed fail to beat the time if the wind is worse.