No, you are thinking about the cascade w/pagination problem. Pagination works with these secondary filters. I just tested it again to be sure.
Not. It gets the galaxy first, but the additional filters and pagination is done on the received galaxy. I see the confusion the pagination is actually applied after the @filter but looking at the order of the syntax it would appear otherwise.
The root function is just to define the smallest part of the galaxy where to start to make the filter better performance to have less data to work through.
Think of it like a logical IF block that only then lets the inner logic fire if it really needs to. This way the @filter is not trying to work on the whole universe, just the nodes in the current galaxy