Why cruisers should not be designed for the battle line

Was Fisher simply asking whether a cruiser had a role in a major fleet battle?

That may have shaped Fisher's thinking, but cruiser design still needed to prioritize presence and trade protection over a place in the battle line.

Fisher may have asked whether a ship could contribute to a major fleet battle. That standard fits battleships better than cruisers. A Napoleonic frigate would usually avoid taking on a ship of the line alone, and a cruiser's characteristic work likewise centered on presence, protection of trade, and other dispersed duties. Designing it around a place in the battle line would neglect those missions.