When is the ‘right’ time to conclude a list of content groups for a Discover/Explore pattern?

I'm working with a client on a Discover/Explore feature for their mobile app. (Think of the pattern used by iTunes, Google Play etc. Essentially grouping the content into interesting categories like 'Top Rated', 'Trending' etc):

The content is location based (tour guides submitted by users.) If you're in a popular area like New York it might have 1000s of tour guides available to show. Whereas a small town might return a handful or none.

My question is about length. Typically you don't see products push this list of groups too far beyond 10 rows. I think they do this to keep it concise and selective. You'd be diluting the curation aspect of the groups if it got too granular and went on forever?

However the client is adamant we should keep showing these groups until we basically run out of content or grouping criteria. Even if that is 25 rows and the app has started presenting them as:

Row 25: Easy New York Tour Guides in an Hour.

Row 26: Medium New York Tour Guides in an Hour. etc

I'm really struggling to articulate to the client why it is a better user experience to keep this list of groups manageable. Has anyone got any previous experience with this type of feature or have further input on the strategy behind them? Thanks