There's more to building your UI than just implementing the design. Even if using this tool all the logic and state management you have to do by yourself.
Putting together the form is the easy part, especially in a large application. You implement your inputs once and re-use them across the app. It's managing the UX and business logic that's hard.
Well I haven't used the tool but I kinda just assumed they would do a good job at this. If all they do is implement each page independently of each other and there's not vue best practices then it's really useless. But I assume it would handle the complexity of the UI.
Putting together the form is the easy part, especially in a large application. You implement your inputs once and re-use them across the app. It's managing the UX and business logic that's hard.