I think it also has something to do with available firepower and the role that they are used for. There was a similar problem, IIRC, with what defined a cruiser in the post-war period, especially with Soviet designs.
In regards to how I know this, I believe I ran into a similar problem whilst researching ship classifications for a forum based game I used to admin, although it was how to define a cruiser rather than a frigate/destroyer, but the same problem has occurred, especially in the Royal Navy.
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