Why Royal Sovereigns are transitional battleships

Were the Royal Sovereigns transitional ships between ironclads and later battleships?

Yes; they mark the transition, and describing them as sovereign battleships avoids defining them only by a future dreadnought standard.

The Royal Sovereigns sit at the transition from ironclad practice to the recognizable late-nineteenth-century battleship. Calling them pre-dreadnoughts can imply that designers built the ships in anticipation of a vessel that did not yet exist. The label defines them backward from HMS Dreadnought rather than from their own technological context. Sovereign battleships instead names the design family that contemporaries could actually see and the new standard it established.