Further testing inspired by this topic & @Nicolas_REMY reveals that a published app produces substantially fewer requests than an app preview, presumably because components are not bundled together in single files and minified for preview pages, but they are for “production” pages.
In my test I looked at network traffic in the browser: loading published app page produces 38 requests, while loading preview page (same page) produces 241 requests. This means that a production app with a small number of users might not be too expensive in the new Scale pricing plan… but when/if developers are previewing pages while working on the app, our pricing increases massively.
So asides from the cumbersome option to move the UI onto an external host, another workaround might be to instruct devs to never click “preview”, and to work on a development container which is always published first and tested at the published URL. Somewhat awkward but maybe ok.
It appears to me that the Scale plan has the (presumably unintended) effect that development on Backendless costs much more than running a production app on Backendless.