Why a steel battleship could sail only after a major redesign

Could a steel warship, including something on Nelson's scale, be driven by sails?

Yes in principle, but a Nelson-sized ship would need a radically different hull layout and an enormous sail plan.

A steel hull can be driven by sails in principle. Applying the idea to a Nelson-class battleship would require much more than fitting masts to the existing design. The hull layout would have to change to carry and balance the rig, and the required sail area would dwarf that of a fully rigged ship of the line. Steel does not rule out wind power, but battleship scale makes it impractical without a comprehensive redesign.