Why a fleet needs battleships more than battlecruisers

If a navy could have only battleships or battlecruisers, which should it choose?

Battleships, because cruisers can cover many battlecruiser missions while no smaller type fully replaces a fast, heavily protected capital ship.

A battlecruiser is a very large cruiser, so a navy without one can still conduct scouting and commerce operations with smaller cruiser types. The battleship's combination of protection and heavy firepower is harder to replace when a fleet must contest a battle line. The chosen battleship should still be as fast as practical. The criticism of the slower Revenge class follows from the view that deliberately accepting less capability in a scarce capital ship shortchanges both the crew and the nation.