answering my own question here…
all categories of a site are listed in /sites.json. so you can use /catgories_and_latest for them main level categories and when you get across the subcategories ids for each main category you pick the subcategory name from the /sites.json response.
I assume there are some props in sites.json that identify a category as main or parent category so in the end /sites.json might be sufficient (one request). haven’t tested yet.