The UPNP ContentDirectory service has two methods Browse() and Search(). Your Control Point will use one or other of these.
The Browse() method loads the data page by page, although the CP itself decides the number of entries in a page. Therefore if a CP sets a page size of (say) 10000 entries, it would have to wait until MC has delivered all of the entries in the first page. Which might take a while.
The Search() method does something like Search Artist =* and again if you have a lot of Artist entries, it has to wait until all are received. In fact, the Search() method also supports a paged response, but again, the page size is set by the CP.
Some of the more clever CPs start with a smaller page size request, and measure how long it takes the server to deliver. And if the first page was delivered fast enough, it increases the page size progressively.
In any case the page sizing is determined primarily by the Control Point and not by the server. i.e. it is not determined by MC. So really you need to refer your question to Bubble or to Samsung.