Nigel, you are mixing feedback of the game itself with the quality of the workouts contained within it. From my perspective, I don’t use Zwift’s built-in workouts at all, so I can’t comment on their quality.
If you can’t hit the anaerobic sprint targets of a workout, why is that the fault of the workout? Being a TrainerRoad user, you should full well know that MANY of their workouts are at least as hard in both TSS and IF. I’ve got a workout coming up this week that is 6x3 minute intervals @ 120%. I’d gladly switch that for only 2x1 @ 150%.
It’s important to note that despite your FTP number, a lot people have a bias to being either better at steady state aerobic efforts or anaerobic sprint-like efforts. So at a given FTP, you may find sweet spot aerobic workouts fairly easy, but VO2Max and above is extremely difficult. Conversely, some people may find long steady intervals very difficult, but find anaerobic intervals much easier.
Another thing to keep in mind… structured training is most beneficial when it’s structured. Jumping around to random workouts may not be all that beneficial. Especially when your body is not used to the stress. This is why TrainerRoad builds up training stress and the type of stress slowly throughout the 20+ week training plans.
Your comment about the cost of your trainer and the testing of Zwift is completely irrelevant. Zwift has been THOROUGHLY tested. On any given hour of the day there are usually 2,000-5,000 riders at a time. That’s incredible to me. Personally, I’ve had very little issues with Zwift. Sure a couple of weird things happen sometimes with riders appearing off course or going through objects… but seriously? You think this compromises your quality of training?!
I use Zwift together with TrainerRoad workouts 4-5 days a week and have logged hundreds of miles so far this winter and have impressively increased my fitness. So yes, I find Zwift to be an excellent training tool. But it’s only a tool. Just like Training Peaks or TrainerRoad. You can build whatever workouts you like for use in Zwift. ZWO Factory is a fantastic (and free) site for building custom workouts, which you can use TrainerRoad, a personal coach, or whatever for… http://zwofactory.com.