The battlecruiser took over the heavy end of the armoured cruiser's job. Light cruisers remained available for duties within their capacity. That split left a gap for stations and missions that needed a larger ship without the demands of a battlecruiser. A large light cruiser, a heavy cruiser or another intermediate design could fill it.
Notable Point · 8:18-9:08
The gap between battlecruisers and light cruisers
As ships that inherited the armoured cruiser's fighting role grew larger, the navy still needed something between them and light cruisers.