The premise is a bit off. Flutter was never just width/height: the model is min/max box constraints. The core rule is: constraints go down, sizes come up, parent sets position.

Row and Column are just layout algorithms built on that same model, not separate engines added later. GridView uses the sliver system internally, but still doesn't require anything like CSS Grid's general layout model. The render API is open enough for custom layouts too, so packages like https://pub.dev/packages/boxy build directly on it