The switch is an iOS system control, and that control can't be resized because it uses images for its rendering.
Web services are better for some use cases. With a shared variable you have to keep some LabVIEW process running which updates the variables, but with web services you can actually fetch data on demand with each call. It's also possible to use web sessions so that you can uniquely identify a running dashboard to distinguish it from another running dashboard (i.e., you can maintain state on the server for each client). Also, you can trigger actions on the server with a web service button, and you can send data from controls as a part of that action.
If you want to poll with web services then you can use the polling web service (right next to the button). The button is meant for on-demand web service calls, and it also allows you to hook up controls to inputs on the web service so you can send data to a web service. You can only use outputs for polling web services, but web service buttons can have both inputs and outputs.
If you want something like a slider where the slider directly controls a running LabVIEW process (without having to press a button after moving the slider) then shared variables are better for that use case.
You can also use security with web services (using NIAuth), but Data Dashboard does not support authentication of any kind with shared variables. That means shared variables are only appropriate for use within a secured network.
