Ofcourse they have their inhouse developers but we musn’t forget the developers at other companies that helped make their systems great (Konami, Capcom, Sunsoft, Hudson, HAL Laboratory, Rare, Argonaut, DMA/Rockstar, etc
Funny how most of these companies are only a shadow of their former selves, with most of the old guard leaving to form their own studios and focus on good games instead of cashgrabs. I absolutely recommend playing Bloodstained – Igarashi is a genius when it comes to MetroidVania