These tools are for simple CRUD apps for people who aren't necessarily strong developers to begin with but need to put together something anyway. That's why the demos focus on speed and only ever show the tiniest of applications.
We're starting to post some larger examples (check out our "download portal" example at https://anvil.works/learn#examples - I'm also working on a video series building a SaaS app over the course of a few hours). But the biggest apps are, of course, our customers', and we can't really publish them as examples.
Their control panel drives companies' entire online marketing operation - creative, targeting, performance, and more - across multiple advertising services. That's a whole lotta UI. Their back end drives the advertising platforms' APIs (eg Google and Facebook), and it all hooks into great big machine learning operations that run on big beefy servers out in EC2. Not just a pretty CRUD app, that's for sure.
(Unfortunately, they know what their services are worth, so I can't just point you at a live demo ;) )
The wonderful thing about the Uplink is that the boundary between "inside Anvil" and "outside Anvil" can be very fuzzy, because you use the same APIs. (See my "escape hatch" post above)