The label pre-dreadnought can hide an important design transition. Earlier battleships remained close to developments of ironclad fleets, while the Royal Sovereign class and its successors form a more mature type immediately preceding Dreadnought. Using Royal Sovereign as the dividing line makes that transition easier to see.
Notable Point · 2:18:06-2:18:44
Why use Royal Sovereign as a battleship dividing line?
The Royal Sovereign class works as a dividing line because the preceding battleships still look like developments of ironclad fleets.