Samsung has multiple such teams.
In my experience with the broader industry, platform teams are usually less than a dozen people who own millions of lines of mostly-external code. You don't usually get the luxury of careful deliberation and comprehensive testing because you're doing too busy putting out fires and chasing down manufacturer errata.
Samsung might be one of the good ones, but sadly most hardware manufacturers treat firmware and software like just another line item on the BOM. Like a screw or a silicon gasket: Source it from some "supplier," spoon it into the product somewhere on the assembly line, and then never touch it again. I've seen a hardware manufacturer that doesn't even use source control or branching. When they have a new hardware product, they take the software that is closest in functionality, hack it until it works with the new hardware, and then set the software back on the shelf until next time.
