You're not wrong. But consider a different lens:

Celeste isn't a game that would need to worry about performance in 2018. It's 2d sprites with box collisions and relatively minimal particle effects. Your toaster can run Celeste.

But a game like Factorio with heavy simulations and complex interactions and pathing absolutely needs to consider performance to pull off a seemless experience.

Those are the kinds of games I'd hope engines like Bevy could enable farther down the line. Design is still key, but some game types are a larger technical challenge than others.