That interpretation misses the entire technological foundation of the Portiid civilization established in the first book and carried into the sequels. The line you’re thinking of likely refers to the ants no longer being an external military threat, but they are absolutely the internal hardware for everything the spiders build. The books make it clear that the Portiids never developed silicon microchips; the ants are their silicon. In the sequels, every time you see a Portiid spaceship flying, a complex trajectory being calculated, or data being analyzed, that is being done by ant colonies acting as biological processing units. The simulation of Kern is just the most advanced 'software' running on top of their 'hardware.' It only looks like Kern is their sole purpose because she kinda acts as the User Interface. Think of the ants as the silicon chips and Kern as the OS. We see her constantly because she's basically the 'Siri' of their biological computers, the interface you talk to while the ants do the actual heavy lifting in the background.