Can you get a backend going for a thousand users fairly quickly and easily? Sure. But that's the WordPress equivalent of describing back end development. If you have any kind of process based workflow with varying parameters, integration with hardware, detailed reporting / analytics, hell, if you even deal with money or dates/ times / timezones, which is any non-trivial application, backend development gets real complex real fast.
It may be trivial to spin up a WordPress site, but it isn't too put together a solid, reliable React / Redux PWA with isomorphic rendering and offline support. It may be trivial to serve a few API endpoints straight out of the database, but it isn't when you have workflows and processes and states and have to deal with shit like GDPR.
> But there's not a ton of serious thinking involved.
Give a fucking break. The only way this could ever be true is if you only have experience working on extremely trivial applications with no complex functionality.