Americans work a lot more hours than most folks in other developed countries on average, including white collar work. And the GP whos assumption you’re buying is wrong: Vivo isnt a new fly by night player, they’re 13 years old and owned by the same massive conglomerate that owns Oppo and OnePlus.
There’s a lot of experience making phones there, and the designs tend to filter up to be white labelable for more recognizable brands.
The parent company is a massive competitors to Apple overall, esp as an OEM and consultant.
This isnt a question of some intrinsic difference in work ethic, it’s another large experienced and well staffed and funded company doing some nice innovation