Why treaty armament does not make a true heavy cruiser

Is the cruiser series simply arguing that bigger ships and more guns are always better?

No. The argument is that many treaty-defined heavy cruisers lacked the dominance expected of the historical heavy-cruiser role.

The criticism of treaty cruisers concerns fighting capability rather than a simple preference for larger ships and more guns. Under this definition, a heavy cruiser should make every lesser cruiser fear engagement while forcing stronger ships to consider their movements carefully. Many treaty ships carrying the legal heavy-cruiser label could not meet that test. Judging them by the older first-class armoured-cruiser role exposes a mismatch between treaty classification and combat power.