Giant is a bit of an anomaly because they ARE the factory., so the line are pretty blurred there. Specialized is also in a unique position as Merida owns 49% of them, so again, the factory owns at least part of the brand.
I can’t speak specifically as to which brands have dedicated offices, but it is an expanding list. I know that one “smedium” sized brand just opened an office in Taiwan, which surprised me a bit. Now, what roles are being fulfilled out of that office, I don’t know
It really depends on the goals of the company and the resources available to them.