Not claiming that all japanese devs are like Nintendo. Just that there is some variety.

Mariko Kart is graphically quite complex for the hardware it's running on, so are Mario games (these maps are neither small nor do they have only few entities). There's a german youtuber who analyses the technical aspects of many nintendo games and given his report: it's amazing how good these games look on the switch.

Optimization is about turning a computationally hard problem into a light algorithm that doesn't take much resources.

Yeah. And Nintendo's first party games look incredible for the hardware they run on.