You talk about how limiting a 5km course is. This is a beta product. Blasting something like the 5km limit when it is well documented that this is just temporary for the beta doesn’t help anyone. This forum, and product, isn’t all roses. But it is place for constructive feedback. What you are providing isn’t that.
I, along with many many others, have found Zwift to be surprisingly motivating even with it’s limitations. I’m getting way better trainer workouts than I have in the past because of how the other “real people” push me.
I also use a Kickr. Initially it was reporting about 20% too high a wattage compared to my SRM. Turns out it was an issue with the Kickr and wahoo fitness, not with Zwift. So if you are having problems with the power, take Zwift Island out of the equation and see if you have the same issues just using the Wahoo Fitness app. If you do, take up your concerns with them.
Zwift is far from perfect at this point but they are listening to their beta users and improving the product. They have already come along ways since the started the Beta and fixed most of the serious problems like crashes.
All that said, it might not be right for you. Seems like your expectations are a bit unrealistic, though, for a beta product.