I wonder if a slightly broader search for existing solutions - for instance, https://defold.com - would have shown that quick-startup, 3d-capable, c-integrable, low-end-hardware performant game engines could have been grabbed off the shelf.

That said, this is cool and I would have probably celebrated a similarly fun project in their shoes. Perhaps the real accomplishment here is getting Toyota to employ you to build a new, niche game engine.

This is specifically designed to embed into Flutter apps, which have specific requirements how they interact with the GPU and renderer.

They already tried other engines, such as Unity. The team didn't just go off and build something without trying existing solutions first.

Having used both, the experience of building actual UI with Flutter is a breeze compared to building UI in any game engine. I can imagine that most of the usage of Flutter is leveraging the huge amount of work that was already done to get efficient and capable UIs done with just a stack of widgets.